Class Xi Chemistry Value Based Questions

Value Addition with Training

CLASS XI

VALUE BASED QUESTIONS WITHOUT ANSWERS

UNIT 1 (BASIC CONCEPTS OF CHEMISTRY)

Q1 Two friends Riya and Pooja were discussing that which is better for expressing the concentration of a

solution: Molality or Molarity ?Pooja told Riya that Molality is considered better for expressing the

concentration as compared to Molarity and explained the reason as well.

(i) What would be the explanation of Pooja?

(ii) What are the units of molarity & molality?

(iii) What is the difference between molality & molarity?

Q2. Mohan learnt the term mol in his chemistry class. He discussed the term mol with her elder sister

Anshika. Anshika explained about and then Mohan got satisfied.

(i) What was the probable answer given by Anshika ?

(ii) What for term mol stands?

(iii) What values are associated with Anshika?

Q3. Radhika ,Supriya and Hema were asked by the PGT chemistry to find the mass of a metal piece

independently one by one using the same balance and same weight box. Each student was asked to

take three observations. The students reported their result as shown in the following table:

Students Results Reported Average

I II III

Radhika 1.325 1.326 1.325 1.325

Supriya 1.320 1.321 1.321 1.321

Hema 1.327 1.329 1.331 1.329

If the actual mass of the metal piece is 1.325g and the permitted uncertainty in the measurement is

0.001g, answer the following questions:

(i) Whose measurement is both accurate and precise? Justify your answer.

(ii) Whose measurement is precise and not accurate Justify your answer?

(iii) Whose measurements are neither accurate nor precise? Justify your answer.

(iv) Mention the associated value or values with these observations.

UNIT2: (STRUCTURE OF ATOM)

Q1.While attending the physics class on optics a student was taught that light with established wave

nature should have particle nature also. Immediately an idea came to the mind of the student that

matter with established particle nature should have wave nature also. After completing his studies he

published a research paper stating the dual nature of matter and later he was awarded NobelPrize for

his work.

(i) Name the scientist who stated the dual nature of matter.

(ii) Give the mathematical statement of the dual nature of matter.

(iii) Write the type of particles for which this principle is applicable.


(iv) Mention the value associated with this principle.

Q2. Guided by Heisenbergs uncertainty principle and de-Broglies theory of dual nature of particles

Schrodinger proposed wave equation. To get proper solution of this equation integer called quantum

numbers were required.

(i) Name the quantum numbers.

(ii) Write the general values assigned to the quantum numbers.

(iii) Mention the value or values associated with wave equation.

Q3. After the discovery of electron and proton Sir J.J. Thomson proposed the plum pudding model of

the atom .But this atomic model was abandoned when Rutherford performed the alpha particle

scattering experiment.

(i) Name the model of the atom proposed by the Rutherford.

(ii) Mention the main features OF THE ATOMIC MODEL proposed by Rutherford.

(iii) Write the value associated with Rutherfords model of the atom.

Q4. Sukumar, a student of class XI science has learnt to write the electronic configuration of the

elements in the chemistry class. Now, He further wanted to know the rules for finding the group

numbers. On the next day he discussed his problem with his teacher. The teacher told his the rules for

finding the group number. Sukumar, then got satisfied.

(i) What rules were told to Sukumar by his teacher?

(ii) What atom is indicated by the following electronic configuration?

(iii) What values are displayed by Sukumar.

UNIT 3 (CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES)

Q1. At present as many as 118 elements are known and the process of discovering new elements is not

yet over. Under the circumstances, it becomes rather impossible to study and remember the properties

of each element. Scientists felt the necessity of group elements of similar characteristics together so

that if the properties of one of them are known, those of the other could be co-related. The real credit

for preparing the periodic table goes to Mendeleev.

(i) Which important property did Mendeleev use to classify the elements in his periodic table

and did he stick to that?

(ii) What is the basic difference in approach between Mendeleevs periodic law and the

Modern periodic law?

(iii) What values are shown by Mendeleev?

Q2. Vimla was taught in chemistry class about electron gain enthalpy. In general, the electron gain

enthalpy for some third period elements (eg.P,S,Cl) are more negative than the corresponding second

period members (eg.N,O,F). Vimla was totally confused and wanted to know the reason for the same.

She discussed with her teacher. The teacher explained the phenomenon which makesVimla satisfied.

(i) What would be the answer of the teacher?

(ii) Which of the following pairs of element has lesser gain electron gain enthalpy? N or O.

(iii) What values are shown by Vimla?


Q3. Name of elements and their atomic symbols were assigned smoothly up to atomic number

103(Lawrencium=Lr). But the problem arose when the element with atomic number 104 was discovered

separately by American and Russian scientists both. Americans Named it Rutherfordium (Rf) While

Russians named it Kurchatovium(Ku). Anyhow, this problem was resolved by assigning digital IUPAC

atomic symbol to the element having atomic number 104 and more. Thus element with atomic number

104 is called Unnilquadium (Uuq).

(i) Write the name and atomic symbol of an element having atomic number 107.

(ii) If the digital atomic symbol of an element is Uun. What is its name and atomic number?

(iii) Mention the value associated with it.

Q4. Mendeleev studied the properties of the elements known at that time and arranged them in to

groups and periods. This arrangement is called Mendeleevs Periodic table. In this table he left some

gaps to be filled by the elements yet to be discovered. When these elements were discovered,

Mendeleev remarked I did not think that I should live to the verification of the law but such was to be

the case.

(i) Name those elements which were discovered later.

(ii) Write the group of each one of these elements in the modern periodic table.

(iii) Mention the associated value with this question.

UNIT 4 (CHEMICAL BONDING AND MOLECULAR STRUCTURE)

Q1. Ice floats on water. Rishabh asked his teacher, why ice is lighter than water? The teacher explained

the phenomenon to Rishabh and He got satisfied.

(i) What would be the answer of the teacher?

(ii) What is the hydrogen bond or hydrogen bonding?

(iii) What values are displayed by Rishabh?

Q2. Two students Saloni and Aditi were discussing about the allotropes of carbon. Saloni asked Aditi

,why one allotrope of carbon is very hard use to make jewellery meanwhile Aditi told Saloni that other

allotrope of carbon is a good conductor and used to make pencils.

(i) Name the above two allotropes of carbon.

(ii) Why one allotrope is conductor and other is not?

(iii) What are allotropes?

(iv) What values are associated with these allotropes?

Q3. The Chemistry teacher was explaining the properties of two hydrides of Sulphur and Oxygen: H2S

and H2O.

H2S and H2O are having same hybridization states but different bond angles. H2S have indefinite

volume while H2O has definite volume. H2S cannot be placed in an open container but H2O can be

placed due to their different physical states.

(i) Write the hybridization states of central atom in H2S and H2O.

(ii) What are the physical states of H2S and H2O?

(iii) Write bond angle of H2O.

(iv) Why H2S and H2O have different bond angles?


(v) Draw the Lewis structures of both the hydrides.

Q4. Rishabh and Sejal were discussing the difference between NF3 and NH3 and both got confused.

Rishabh and Sejal asked their subject teacher, why NF3 and NH3 have different dipole moment while

both are having same hybridization states and same number of lone pair of electrons.

UNIT 5(STATES OF MATTER)

Q1. Chemistry teacher was teaching the three variables Pressure (p), Temperature (T) and Volume (V) to

XIthclass students. He taught to students that there are three laws which deals with the properties of

gases at various variables keeping one of them constant.Suddenly one of them asked teacher, how can

we draw the graph between two variables keeping third one constant.

(i) Name the gas law with the properties of the gases at constant pressure.

(ii) Which law deals the properties of the gases at constant temperature?

(iii) What is the Amontons law?

(iv) What value is associated with this concept?

Q2. Sejal asked Saloni that why people are undergoing medical check-up before going on AMARNATH

YATRA. Saloni explained the reason to Sejal and she got satisfied meanwhile Rishabh told that liquid

boils at lower temperature at a Hilly station than in a plane area.

(i) What reason was explained by Saloni to satisfy Sejal?

(ii) Why does liquid boil at lower temperature at Hilly station?

(iii) What value is associated with Saloni?

(iv) Mention the value Associated with concept of Rishabh?

Q3. One day Seema and Smriti decided to cook the food at a hill station.Seema takes a pan to cook food

while Smriti started cooking the food in a pressure cooker at the same place.

(i) Who will cook rice faster?

(ii) What is the effect of pressure on boiling point?

(iii) Pressure is lower or higher at hill station?

(iv) What value is associated with the pressure of cooking food in different vessels?

UNIT 6 (THERMODYNAMICS)

1. The teacher taught in the class when an ideal gas expands, there is no change in temperature. On the other hand, when a real gas expands, cooling in produced. Ram, a student of the same class was curious to know its reason. The teacher explained the reason and Ram got satisfied.

(a) What would be the answer of the teacher? (b) For a reaction both DH and DH are negative under what conditions the reaction

occurs spontaneously? (c) What values are displayed by Ram?

2. In general, an exothermic reaction is thermodynamically spontaneous. Seema was curious to know under what circumstances and exothermic reaction may not be


thermodynamically spontaneous. She discussed her problem with her friend Nidhi who explained her in detail and Seema got satisfied. (a) What would be the answer of Nidhi? (b) For a reaction both DH and DS are positive under what conditions the reaction

occurs spontaneously? (c) What values are displayed by Nidhi?

3. While teaching the concept of irreversible process the teacher noticed that some students of the class are restless because they were unable to grasp the subject. Then she recited a nursery shyme Humpty Dumpty sat on a wall, Humpty Dumpty had a great fall. All the kings horse and all the kings men could not put Humpty Dumpty together again. The students became cheerful and convinced.

(a) Name two irreversible natural processes. (b) Mention the value or values associated with the above process.

4. Reversible process is slow but every slow process need not be reversible. (a) Give an example with justification of a slow process which is not reversible. (b) Write the associated value with your answer.

5. Some thermodynamic properties are related in the same way as total money earned money paid as income tax and the money available for other purposes. (a) Name these thermodynamic properties (b) Write the relation or relations between these thermodynamic properties (c) Mention the associated value with it.

UNIT 7 (EQUILIBRIUM)

1. In group III, the cat ions Fe,Cr and Al are precipitated as hydroxides by the addition of NH4OH to the aqueous solution of the mixture. But a small amount of NH4Cl is added before the addition of NH4 OH. Arvinder was confused to see why common NH4+ ion is added? He asked his friend Palvinder the purpose of adding common NH4+ ion. Palvinder explained the purpose of adding NH4Cl and then Arvinder got satisfied.

(a) What would be the answer of Palvinder. (b) Why magnesium is not precipitated from a solution of its a salt by NH4OH in the

presence of NH4Cl. (c) What values are shown by Palvinder?

(2) There is a fizz when a soda water battle is opened. Kusum was very curious to know its

reason. She discussed her problem with her elder sister Monika. Monika explained Kusum the

whole phenomenon and then Kusum got satisfied.

(a) What would be the answer of Monika?

(b) Solubility of a Ca (CH3COO)2 decreases with rise of temperature while that of

Pb (NO3)2 increases with rise of temperature.

(c) What values are shown by Kusum and Monika?

3.A solution has the capacity to resist the change in its PH when a small amount of a strong

acid or strong base is added to it. These solutions may be acidic or basic or neutral in

nature.

(a) Name this solution and give a general example.


(b) Select the components to prepare this type of solution having PH between 4 and 5.

(c) Mention the value associated with this type of solution. 4. Ammonia is an important compound. It is manufactured by Habers process. In

this process nitrogen and hydrogen combine to produce ammonia in the presence of a catalyst.

2 + 2 23()

(a) What is the source of nitrogen in Habers process? (b) What is the effect of increase of temperature on the equilibrium yield of

ammonia? Justify your answer. 5. The teacher gave the samples of milk, black coffee, tomato juice, lemon juiced

and egg white to two groups of students and asked them to find the PH value of each sample and arrange them in the order of decreasing PH values. They reported the PH values as fallen.

Group A : Egg white Milk Black Coffee Tomato Juice, Lemon Juice

Group B: Egg white Black Coffee Tomato Juice, Lemon Juice

(a) Which group of students reported the correct decreasing order? (b) Which sample has the highest PH value? Is it acidic or basic or neutral in nature? (c) mention the value associated with the PH measurement

UNIT 8 (REDOX REACTIONS)

1. Redox reactions are involved in chemical, industrial and biological processes. When the chemistry teacher taught the redox reactions with reference to electrochemical cells the students were not able to grasp the relation between anode, cathode, oxidation and reduction. To convince the students the teacher told them to remember the sequence English alphabets.

(a) How is sequence of English alphabets helpful to know the electrodes where oxidation and reduction take place?

(b) Write the associated value this problem. (2) Fuels acts as source of energy. In the selection of fuel, its calorific value,

economy and environmental effects are taken in to consideration. Hydrogen gas is such a fuel which has high calorific value and its combustion product does not have any harmful environmental effect. Still hydrogen is not suitable as domestic fuel.

(a) Why is hydrogen not considered as a suitable domestic fuel. (b) Write the combustion reaction of hydrogen. (c) Name device where hydrogen and oxygen are used to produce energy. (d) Mention the associated value with this question. 2. Yash Pal was totally confused to learn that phosphorous acid can act both as

oxidizing agent as well as reducing agent while phosphoric acid is only an oxidizing agent. He discussed this problem with his friend Akbar. Akbar explained the phenomenon to his satisfaction.

(a) What examination did Akbar give to Yash Pal? (b) in the reaction :-

MnO2 + 4HCl MnCl2 + 2H2O +Cl2


(c) What values are attached to this explanation? 3. A solution of an electrolyte can be stored in a particular vessel only in case there

is no chemical reaction taking place with the material of the vessel. The teacher asked a student Achin, is it possible to store silver nitrate in copper vessel. Achin explained the teacher; it is not possible to store silver nitrate in copper vessel. Achin explained the teacher; it is not possible to store silver nitrate in copper vessel and gave his explanation.

(a) What explanation did Achin gave to his teacher. (b) What is oxidation according to electronic Concept? (c) What values displayed by Achin?

UNIT 9 (HYDROGEN)

1. Prakash was surprised to see that air painting get furnished. Prakash discussed this matter with his elder brother Manoj. He also wanted to Manoj explained him the reason and also the method to restore the original whiteness.

(a) Can you predict what explanation was given by Manoj? (b) Analyse the attitude of both Prakash and Manoj? (c) H2O2 act as an oxidizing agent as well as reducing agent. Why? 2. Teacher told the students that water should that water should be softened

before using in boilers. Karina one of the students, asked the reason. The teachers explained the reason in detail to him and then Karina got satisfied.

(a) Predict the explanation given by the teacher. (b) Temporary hard water becomes soft on boiling. Why? (c) What values are displayed by Karina. 3. Hard water is unfit for its use in the laboratory and laundry because of the

presence of chlorides of calcium and magnesium. One way to remove these ions from hard water is the use of sodium carbonate. Your teacher asked you to calculate the amount of sodium required to remove the calcium ions from a sample of hard water which is 0.002 M in calcium ions. (a) Write the reaction of sodium carbonate in the removal of hardness of

water. (b) What mass of sodium Carbonate is required to remove the calcium ions from

a sample of 1000 litres of hard water? (c) Write the value associated with this problem.

4. A compound of hydrogen and oxygen has empirical formula OH. This compound is used to restore the colour of old oil paintings containing lead oxide. This compound also liberates iodine from an acidified solution of potassium iodide.

(a) Name this compound and write its formula. (b) Write a balanced chemical equation to show the restoration of colours of the old

painting by this compound. (c) Mention the value associated with the function of this compound.


UNIT 10 (s BLOCK ELEMENTS)

1. Om Prakash was studying the trend of solubility of alkaline earth hydroxides in water.

By doing actual experiments, he came to know that the solubility of hydroxides of alkaline

earth metals in water increases down the group i.e. Be(OH)2 is least soluble while Ba (OH)2

maximum soluble in water. He discussed this problem with his classmate Anil. He explained the

phenomenon and Om Prakash got satisfied.

(a) What explanation did Anil give to Om Prakash? (b) What values are attached to this explanation?

(c) Ba(OH)2 is soluble in water while BaSO4 is almost insoluble. Give reason. 2. During his experiments, Rajender found that sodium can be used to dry diethyl ether

but not ethyl alcohol. Rajender wanted to know the reason behind it. Therefore he asked his friend Annu about this problem. Annu explained the chemistry behind it and Rajender got satisfied.

(a) What explanation did Annu gave to Rajender? (b) Sodium is found to be more useful than potassium. (c) What values are displayed by Annu?

3. Quicklime is an important compound. It is prepared by thermal decomposition of limestone in tall furnaces called kiln. During such an operation the top of the Chimney of the kiln was closed. After one week when the kiln was opened it was observed that very little lime was formed. The workers reported the poor result to the Production engineer who suggested them to increase the height of the chimney. This time also there was no improvement in the production of lime. Ultimately the production Engineer approached his forms chemistry and narrated the problem. The professor suggested him to keep the top of the chimney opened. This helped.

(a) Represent the thermal decomposition of lime stone by a chemical equation. (b) Why was the production of lime not satisfactory when the top of the chimney

was closed? (c) How did the suggestion of the professor help in the improvement of the

production of lime? (d) Mention the associated value with this incidence.

VALUE BASED QUESTIONS WITH ANSWERS

UNIT 11 (p - BLOCK ELEMENTS)

1. One of the elements of group 13 was not known at that time when Mendeleev gave his periodic

table. This element has some interesting properties much different from other elements of this group.

Now answer the following questions:

(i) Name the element which was not known at Mendeleevs time.

(ii) Mention its interesting properties.

(iii) Give its one use.

Ans: (i) Gallium


(ii) It can melt at 303 K but it does not boil up to 2676 K.

(iii)Used as semi-conductor.

2. Kevlar is a nylon obtained by condensation polymerisation of 1,4- diaminobenzene and 1,4-

benzenedicarboxylic acid. Its fibre is five times stronger than steel and hence are used for making bullet-

proof vests. There are two compounds of boron which are also used for making bullet-proof vests.


(i) Name the two compounds of boron used for making bullet-proof vests and how are they

prepared?

(ii) What are the advantages of using boron based compounds over Kevlar?

Ans: (i) Boron nitride (BN) and Boron carbide (B4C)

B2O3(s) + 2NH3 2 BN (s) + 3H2O (g) (At 1173 K)

2 B2O3(s) + 7 C (s) Electric furnace -- B4C (s) + 6CO (g) (At 1873 K)

(ii)Boron has high ability to absorb neutrons and hence these two boron compounds can act as

protective shield against radioactive radiations.

UNIT 12 (Some Basic Concept in Organic Chemistry)

1. Three students Vaibhav,Vishal and Vikas were determining the elements present in given organic

compound by Lassaignes test. Vaibhav added FeSO4 and dil. H2SO4 acid to Na- extract and observed

Prussian blue colour. Vishal was keeping some pieces of sodium metal in his pocket, Vikas asked him

not to do so. Now answer the following questions.

(a) Name the element present in the organic compound.

(b) Write the test for chlorine

(c) Write the value associated.

Ans: (a)Nitrogen

(b) sodium fusion extract + silver nitrate solution = white ppt

(c)Scientific attitude/concern for others

2. An organic compound on heating changes directly into vapours without undergoing into liquid state,

it is insoluble in water and is commonly used to prevent clothes against moths. It is contaminated with

cinnamaldehyde.Naresh, a student of class XI was asked by his teacher how to purify it.Now answer the

following questions

(i) Which method of purification would Naresh apply?

(ii) Name the compound and write its another use.

(iii) Write the value associated with this.

Ans: (a) Sublimation

(b) Naphthalene and can be used as freshener


(c) Scientific attitude

3. Carbon shows a unique property to form a large number of organic compounds. Even towards the

end of 19th century the number of organic compounds known was difficult to remember by their

common names. In order to systematize the naming of organic compounds IUPAC system of

nomenclature was first introduced in 1947and is modified from time to time. Based on these facts now

answer the following questions:

(i) Name the property of carbon to link itself to form a large number of compounds.

(ii) Write the IUPAC name of CH3 CH=CH CH (Br) CH3 and trivial name of CH3 C (CH3)2 CH3.

(iii) Write the value associated with property of carbon.

Ans.(i) Catenation

(ii) 4-Bromopent-2-ene, Neo-pentane (iii) integration / group works

UNIT 13 (HYDROCARBONS)

1. Saturated aliphatic hydrocarbons are called alkanes.They are mainly used as fuels. Depending upon

their physical properties such as boiling point, density, solubility, they have many other uses. Now

answer the following questions.

(a)Out of propane and butane why is propane used as fuel for barbecue grill?

(b)Which alkane is used in cigarette lighters?

(c)What is mineral oil? Give its uses.

(d)What are the uses of solid alkanes?

(e)What is Vaseline? What are its uses?

Ans. (a) Barbecue is usually done in open. In cold countries, although both propane and butane can be

used but propane is preferred because it works better at low temperatures. The reason being that due

to lower boiling point (231K), propane always remains as gasin the cylinder in spite of cooling produced

byJoule Thomson effect during its use and thus ensures a constant supply of gas.Incontrast,butane due

to its higher boiling point(272.5K)and cooling produced by Joule-Thomson effect,it becomes a liquidin

the cylinder and thus the supply of gas becomes slower and slower as the gas is being used.

(b) Butane is used in cigarette lighters since it can be easily liquefied at room temperature.

(c)Mineral oil is a mixture of liquid alkanes containing 16-18 carbon atoms and is used as a laxative and

as a lubricant.

(d)Alkanes with 18 or more carbon atoms are waxy solids. These are used as waxy coatings on fruits and

vegetables to help them to retain moisture, inhibit mould growth and enhance appearance.

(e)Vaseline is a mixture of solid alkanes having low melting points. It can prevent moisture loss and

chapped lips and soften nail cuticles.It is also used in ointments and cosmetics.


2.Benzene is the simplest and ideal aromatic compound. It is also one of the most basic petrochemicals.

It is mainly used to prepare a number of important chemicals such as toluene, phenol, aniline,

biphenyletc which are used in the manufacture of dyes, detergents, drugs, explosives, pesticides,

rubbersandlubricants.But it is carcinogenic. Now answer the following questions.

(a)Mention 3 uses of benzene in petrochemical industry.

(b)Why benzene is used as additive in gasoline?

(c)Comment on the bad effects and carcinogenicity of benzene.

(d)In view of toxicity and carcinogenicity of benzene, should its production be banned? Give your

suggestions.

Ans(a)Benzene is mainly used as an intermediate to make other chemicals. About 85 of benzene is

consumed in the production of 3 chemicals, ethyl benzene, cumene and cyclohexane. Ethyl benzene is a

precursor to styrene, which is used to make polymers and plastics. Cumene is converted to phenol and

acetone.

Cyclohexane is used to manufacture nylon.

(b)Because of its high octane number and anti-knocking properties benzene is used as an additive in

gasoline.

(c)Exposure of benzene vapours to humans is a global problem. It affects liver, kidney, lungs and heart.

Benzene increases the risk of cancer and other illness. In the body, it gets oxidized to benzene oxide

which is not excreted readily and can interact with DNA to produce harmful mutations. Benzene is also a

notorious cause of bone marrow failure.

(d)Although benzene is a potential carcinogen, its production cannot be banned because its wide

spread application in the manufacture of dyes, detergents, nylons, explosives and

pesticides.Instead,benzene should be used in fuming cupboards and ventilated laboratories.

Q.3 Kamala and Reena are best friends. One evening Kamala went to Reenas house and found her in

the kitchen. She saw that the burner was emitting yellow flame and a black soot was getting deposited

on the bottom of the cooking vessel .She advised Kamala to put off the gas and helped her in cleaning

the holes of the burner. The gas was then switched on and they found that the burner was now emitting

clean blue flame.

(i) Why was the burner emitting yellow flame?

(ii) What was the purpose of cleaning the holes of the burner?

(iii) What value is expressed by Kamala?

Ans. (i) The holes of the burner were blocked due to soot or some oily material. This caused incomplete

combustion of the fuel

(ii) By cleaning the holes of the burner the deposits were removed which led to the complete

combustion of the fuel.

(iii) Kamala helped her friend in saving fuel and in preventing wastage of gas.


UNIT 14 (ENVIRONMENTAL CHEMISTRY)

1. Environmental pollution is causing a serious threat on the earth.Due to combustion of fossil

fuels, a number of poisonous and harmful gases enter into the atmosphere.Every country has

made strict laws for industries and individual citizens to keep pollution under control.


(i) Why is it advised not to sleep with burning coke angithi in a closed room on winter nights?

(ii) How does the combustion of motor fuels cause pollution of the atmosphere?

(iii) Name one natural source and one human activity by which SO2 enters into atmosphere?

Ans: (i) On burning coke, a lot of carbon monoxide is produced which causes anoxia.

(ii)On burning motor-fuels, toxic oxides of nitrogen is formed which affect respiratory system.

(iii)Due to volcanic eruption and through combustion of sulphur containing fuels.

2. An ozone-layer is present at a height of 25-30 km from earth-surface which protects us from

U.V. radiation.A hole in the ozone-layer is created due to human activity.


(i) Which activity has been causing ozone-hole?

(ii) What is the most serious effect of ozone-hole?

(iii) What hasbeen done to protect ozone layer?

(iv) How does excess CO2 gas pollute the atmosphere?

Ans: (i) Use of CFCs

(ii)The most serious effect is that U.V. radiation reaches the earth-surface causing skin cancer.

(iii)Use of CFCs has been banned.

(iv)Excess CO2 creates greenhouse effect which increases the earths temperature.

*****

Documents

Class Xi Chemistry Value Based Questions