Science: 2013: CBSE: [Delhi]: Set – I

Modern periodic table has 18 vertical columns and they are called as ‘Groups’.

Speciation is as an evolutionary process which involves the formation of new species from the existing species.

Biodegradable and non- biodegradable wastes should be discarded in two separate dustbins for proper management of wastes. Biodegradable and non- biodegradable wastes differ in their natural composition and hence, are degraded in different ways. Biodegradable wastes are degraded naturally by the action of microorganisms present in the soil, while non-biodegradable wastes are melted and reused.

Somatic cells of human beings have 23 pairs of chromosomes. The number of chromosomes in the gametes, arising from the germ cells, is half the number of chromosomes in the somatic cells of the body. When these gametes combine during fertilisation, the original chromosome number is restored in the zygote. The zygote develops into complete individual having same chromosome number as parent.

Below given is the ray diagram in which the ray EF is the incident ray and GH 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 two advantages associated with water harvesting at community level are:

• It helps to overcome the scarcity of water.
• It helps in reducing the effects of droughts and floods.

The main product formed during the reaction is Ethene along with water.

The structure of ethene is as follows
      

In this reaction, H₂SO₄ acts as a dehydrating agent. Therefore, ethanol undergoes dehydration i.e., loses a water molecule to form ethene.

Homologous series of carbon compounds are so called because in such a series of compounds, the same functional group is present which decides the properties of the carbon compound irrespective of the length of the carbon chain. The two consecutive members of a homologous series of alcohols are CH₃OH and C₂H₅OH

(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

(i)The electronic configuration shows ₁₉K 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.