Class 10 Science CBSE 2013 Solved Questions
How many horizontal rows are there in the modern periodic table and what are they called? (2013)
Ans: There are 7 horizontal rows in the modern periodic table. They are called periods.
List any two factors that could lead to speciation. (2013)
Ans: Geographical isolation and genetic drift could lead to speciation.
Mention one negative effect of our affluent life style on the environment.
Ans: Exploitation and overconsumption of natural resources will ultimately result in their scarcity.
Mention two functions of the human testis.
Ans : 1. They produce male germ cells i.e., sperms.
2. They act as endocrine glands and secrete the hormone testosterone which controls secondary sexual characters in males.
Every one of us can do something to reduce our consumption of various natural resources. List four such activities based on the 3-R approach.
Ans. 1. Use of materials such as paper should be preferred as they can be reused and recycled.
2. Materials like glass and some plastics can be recycled on heating and get easily converted into different products like toys, containers which can be reused again.
3. e-wastes such as unused computers, mobiles etc. can be repaired and used again.
4. Household wastes such as vegetable wastes etc. can be used as manure for plants.
‘A ray of light incident on a rectangular glass slab immersed in any medium emerges parallel to itself.’ Draw a labelled ray diagram to justify the statement.
Ans. When a ray of light is incident on a rectangular glass slab immersed in a medium, the emergent
ray comes out parallel to the incident ray.
We often observe domestic waste decomposing in the bylanes of residential colonies. Suggest
ways to make people realise that the improper disposal of waste is harmful to the environment.
Ans. Some of ways to make people realise that the improper disposal of waste is harmful to the
environment are:
1. Improper disposal of waste will serve as a breeding ground for mosquitoes and will create favourable conditions for the spread of various diseases.
2. Improper disposal of waste will release harmful gases in the environment which makes the environment unclean and unhygienic for normal living of organisms.
3. The waste will flow to water bodies along with the rain water and become a threat to aquatic organisms.
Name the oxidising agent used for the conversion of ethanol to ethanoic acid. Distinguish
between ethanol and ethanoic acid on the basis of (i) litmus test, (ii) reaction with sodium carbonate.
Ans. Alkaline potassium permanganate (KMnO4) or acidified potassium dichromate (K2Cr2O7) can be used as an oxidising agent for conversion of ethanol to ethanoic acid.
Litmus test: Ethanoic acid turns blue litmus solution red whereas ethanol being neutral in nature has no effect on litmus solution.
Reaction with sodium carbonate: Ethanoic acid reacts with sodium carbonate to form sodium ethanoate and carbon dioxide gas is evolved.
2CH3COOH + Na2CO3 --> 2CH3COONa + H2O + CO2
Ethanol does not react with sodium carbonate.
CH3CH2OH + Na2CO3 --> No reaction
Differentiate between alkanes and alkenes. Name and draw the structure of one member of each.
Ans. Alkanes: Hydrocarbons in which the carbon atoms are joined by single covalent bonds are called Alkanes. They have general formula CnH2n+2, where n is the number of carbon atoms. Suffix, -ane is used while naming alkanes.
Alkenes: Hydrocarbons in which the carbon atoms are joined by a double bond are called Alkenes. They have general formula CnH2n, where n is the number of carbon atoms. Suffix, -ene is used while naming alkenes.
Alkanes generally burn with clean flame. Why?
Ans. Alkanes generally burn with clean flame because in them, the percentage of carbon is comparatively low as compared to other unsaturated hydrocarbons. Hence they get oxidised completely by the oxygen present in air.
Given below are some elements of the modern periodic table:
4Be, 9Fe, 14Si, 19K, 20Ca
i. Select the element that has one electron in the outermost shell and write its electronic configuration.
ii. Select two elements that belong to the same group. Give reasons for your answer.
iii. Select two elements that belong to the same period. Which one of the two has bigger atomic size?
Ans. i. 19K has one electron in the outermost shell and its electronic configuration is
2, 8, 8, 1.
ii. 4Be and 20Ca belongs to same group i.e., Group 2.
Electronic configuration:
4Be – 2, 2
20Ca – 2, 8, 8, 2
4Be and 20Ca have same number of valence electrons in outermost shell i.e., 2 so they belong to same group.
iii. 9F and 4Be belongs to the same period i.e., period 2.
Electronic configuration:
9F - 2, 7
4Be - 2, 2
4Be has a bigger atomic size than 9F because the atomic radius decreases as we move from left to right in a
period due to increase in nuclear charge which tends to pull the electrons closer to the nucleus and hence
size of atom reduces.
Ans: There are 7 horizontal rows in the modern periodic table. They are called periods.
List any two factors that could lead to speciation. (2013)
Ans: Geographical isolation and genetic drift could lead to speciation.
Mention one negative effect of our affluent life style on the environment.
Ans: Exploitation and overconsumption of natural resources will ultimately result in their scarcity.
Mention two functions of the human testis.
Ans : 1. They produce male germ cells i.e., sperms.
2. They act as endocrine glands and secrete the hormone testosterone which controls secondary sexual characters in males.
Every one of us can do something to reduce our consumption of various natural resources. List four such activities based on the 3-R approach.
Ans. 1. Use of materials such as paper should be preferred as they can be reused and recycled.
2. Materials like glass and some plastics can be recycled on heating and get easily converted into different products like toys, containers which can be reused again.
3. e-wastes such as unused computers, mobiles etc. can be repaired and used again.
4. Household wastes such as vegetable wastes etc. can be used as manure for plants.
‘A ray of light incident on a rectangular glass slab immersed in any medium emerges parallel to itself.’ Draw a labelled ray diagram to justify the statement.
Ans. When a ray of light is incident on a rectangular glass slab immersed in a medium, the emergent
ray comes out parallel to the incident ray.
We often observe domestic waste decomposing in the bylanes of residential colonies. Suggest
ways to make people realise that the improper disposal of waste is harmful to the environment.
Ans. Some of ways to make people realise that the improper disposal of waste is harmful to the
environment are:
1. Improper disposal of waste will serve as a breeding ground for mosquitoes and will create favourable conditions for the spread of various diseases.
2. Improper disposal of waste will release harmful gases in the environment which makes the environment unclean and unhygienic for normal living of organisms.
3. The waste will flow to water bodies along with the rain water and become a threat to aquatic organisms.
Name the oxidising agent used for the conversion of ethanol to ethanoic acid. Distinguish
between ethanol and ethanoic acid on the basis of (i) litmus test, (ii) reaction with sodium carbonate.
Ans. Alkaline potassium permanganate (KMnO4) or acidified potassium dichromate (K2Cr2O7) can be used as an oxidising agent for conversion of ethanol to ethanoic acid.
Litmus test: Ethanoic acid turns blue litmus solution red whereas ethanol being neutral in nature has no effect on litmus solution.
Reaction with sodium carbonate: Ethanoic acid reacts with sodium carbonate to form sodium ethanoate and carbon dioxide gas is evolved.
2CH3COOH + Na2CO3 --> 2CH3COONa + H2O + CO2
Ethanol does not react with sodium carbonate.
CH3CH2OH + Na2CO3 --> No reaction
Differentiate between alkanes and alkenes. Name and draw the structure of one member of each.
Ans. Alkanes: Hydrocarbons in which the carbon atoms are joined by single covalent bonds are called Alkanes. They have general formula CnH2n+2, where n is the number of carbon atoms. Suffix, -ane is used while naming alkanes.
Alkenes: Hydrocarbons in which the carbon atoms are joined by a double bond are called Alkenes. They have general formula CnH2n, where n is the number of carbon atoms. Suffix, -ene is used while naming alkenes.
Alkanes generally burn with clean flame. Why?
Ans. Alkanes generally burn with clean flame because in them, the percentage of carbon is comparatively low as compared to other unsaturated hydrocarbons. Hence they get oxidised completely by the oxygen present in air.
Given below are some elements of the modern periodic table:
4Be, 9Fe, 14Si, 19K, 20Ca
i. Select the element that has one electron in the outermost shell and write its electronic configuration.
ii. Select two elements that belong to the same group. Give reasons for your answer.
iii. Select two elements that belong to the same period. Which one of the two has bigger atomic size?
Ans. i. 19K has one electron in the outermost shell and its electronic configuration is
2, 8, 8, 1.
ii. 4Be and 20Ca belongs to same group i.e., Group 2.
Electronic configuration:
4Be – 2, 2
20Ca – 2, 8, 8, 2
4Be and 20Ca have same number of valence electrons in outermost shell i.e., 2 so they belong to same group.
iii. 9F and 4Be belongs to the same period i.e., period 2.
Electronic configuration:
9F - 2, 7
4Be - 2, 2
4Be has a bigger atomic size than 9F because the atomic radius decreases as we move from left to right in a
period due to increase in nuclear charge which tends to pull the electrons closer to the nucleus and hence
size of atom reduces.
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