Science:2015:CBSE:[Delhi]:Set-I

C_nH_2n is the general formula for the alkene series. The second member of the alkene family is ethene having formula C₂H₄.

The functions performed by the testis in human beings are:
1. Secretion of testosterone hormone
2. Production of sperm

The ozone layer in the atmosphere protects the Earth surface from the ultraviolet rays radiating from the sun. The ultraviolet radiation is very harmful for living organisms and can cause skin cancer in human beings.

The following are the four characteristics of the images formed by plane mirrors:
1. The images formed by plane mirror are of the same size as the size of objects.
2. The images formed by plane mirror are at the same distance behind the mirror as the distance of objects from mirror.
3. The images are laterally inverted.
4. The images formed are virtual and erect.

The forests are considered as “Biodiversity hot spots” because the parameter for the biodiversity is the number of species found in that area and forest have high species diversity.

The two ways by which an individual can contribute effectively to the management of forests and wildlife are:

Avoid throwing non bio-degradable wastes in the forest protected area.

Reduce the use of the products that are directly derived from the forest, like wood.

Sustainable management means the use of the natural resources in such as a way that it is used by present generation and future generation.

Reuse is considered better than recycling because it does not require money and energy and also results in less air and water pollution.

The process of adding hydrogen to an unsaturated compound is known as hydrogenation. For example, hydrogenation of ethyne:

Conditions for hydrogenation are:

i) An unsaturated compound

ii) A suitable catalyst

iii) A reactant molecule which is to be added to the unsaturated hydrocarbon

During hydrogenation of vegetable oils, liquid saturated fatty acids are converted into solid saturated fatty acids.

Soap molecules are sodium or potassium salts of long-chain carboxylic acids or higher fatty acids. They form scum upon reaction with calcium and magnesium ions present in hard water.

Detergent molecules are ammonium or sulphonate salts of long-chain carboxylic acids. They do not form insoluble precipitates with calcium and magnesium ions.

Cleansing action of soaps: The dirt or oil droplet present on clothes is organic in nature and is insoluble in water. Hence, it cannot be removed by only washing with water. When soap is dissolved in water, its hydrophobic ends attach themselves to the dirt. Then, the molecules of soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster. These micelles remain suspended in the water. When cloth is rinsed in water, the dirt particles are easily washed away.

There are 18 groups and 7 periods in modern periodic table.

(a) Atomic size and metallic character increases down the group.

(b) Atomic size and metallic character decreases from left to right in a period.

(i) Among the given elements, ₁₉K has one electron in the outermost shell as its electronic configuration is 2, 8, 8, 1.

(ii) The elements ₄Be and ₂₀Ca belong to the same group, i.e., Group 2 as both elements have two electrons each in their outermost shells.

Electronic configuration of ₄Be = 2, 2.
Electronic configuration of ₂₀Ca = 2, 8, 8, 2.

(iii) The atomic number of element X = 17
Electronic configuration of element X = 2, 8, 7.
Number of valence electrons in X = 7
Valency of X = 8 − 7 = 1

Similarly, Atomic number of element K = 19

Electronic configuration of K is 2, 8, 8, 1.
Number of valence electron in K = 1
Valency of K = 1

Therefore, on combining the elements K and X, we get the formula of compound as KX.

The compound KX is of ionic nature.