Science: 2013: CBSE: [Delhi]: Set – II

Modern periodic table has 7 horizontal rows and they are called as ‘Periods’.

The two factors which could lead to speciation are natural selection and genetic drift.

One negative effect of our affluent life style on the environment is global warming. It has resulted due to excess release of greenhouse gases from vehicles, industries in the environment etc.

The two functions of human testis are:

1. It produces male gametes (sperm).
2. It secretes testosterone which is responsible for the development of secondary sexual characteristics in males.

3R strategy is an approach to reduce the amount of solid waste. It stands for reduce, recycle and reuse. Four activities based on 3-R approach are:

1. Avoid the use of plastic or polythene bags as they are non-biodegradable. So, they pollute the environment.
2. Prefer the use of paper bags as they can be recycled and reused.
3. Switch off the electrical appliances when not in use in order to reduce the electricity consumption.
4. Use the reverse side of paper and envelope in order to save paper.

EO is the incident ray and O’H is the emergent ray, which is parallel to the incident ray.

Improper disposal of waste is harmful to the environment as:

1. Improper disposal of waste serves as breeding ground for mosquitoes, which leads to the spread of diseases.
2. Improper disposal of waste also leads to release of harmful gases into the environment.

The oxidising agent used for the conversion of ethanol to ethanoic acid is alkaline potassium permanganate or acidified potassium dichromate.

The difference between ethanol and ethanoic is as follows:

1. Litmus paper

Ethanol does not show any change in the colour of litmus paper whereas ethanoic acid turns blue litmus paper red as it is acidic in nature.

2. Sodium carbonate

Ethanol does not give any reaction with sodium carbonate.

Ethanoic acid reacts with sodium carbonate to form sodium ethanoate, water and carbon dioxide gas.

 

(a) The difference between alkanes and alkenes is as follows:

(b) Alkanes (saturated hydrocarbons) will generally burn with a clean flame because saturated compounds contain comparatively less percentage of carbon which get completely oxidised by the oxygen present in the air. On the other hand, the percentage of carbon in unsaturated compounds is more and it requires more oxygen to get completely oxidised. Hence there is insufficient supply of oxygen for combustion of unsaturated hydrocarbons.

(i)Electronic configuration of ₄Be =2,2

Electronic configuration of ₉F =2,7

Electronic configuration of ₁₄Si =2,8,4

Electronic configuration of ₁₉K =2,8,8,1

Electronic configuration of ₂₀Ca=2,8,8,2

The electronic configuration shows₁₉K has one electron in the outermost shell.

(ii) Since, ₄Be and ₂₀Ca both have two electrons in the valence shell, therefore, they belongs to same group i.e. Group-2.

₄Be – 2, 2

₂₀Ca- 2, 8, 8, 2

 (iii) ₉F and ₄Be belongs to the same period, Period 2 because both of them have same number of shells.

₉F – 2, 7

₄Be – 2,2

₄Be has bigger atomic size then ₉F because the atomic radius decreases as we move from left to right due to increase in nuclear charge which pulls the electrons closer to the nucleus.