Science: 2012: CBSE: [Delhi]: Set – I

(i) The functional group present in C₂H₅Cl is Chloro

(-Cl).

(ii) The functional group present in C₂H₅OH is alcohol

(-OH).

Dispersion of light does not take place when there is no atmosphere. Thus, the colour of the sky will be black when it is observed from a place where atmosphere is absent.

Chlorofluorocarbons (CFCs) released from refrigerants and air-conditioner is linked to the decrease in the amount of ozone in the upper atmosphere of the earth.

Bacteria and fungi are called decomposers because they breakdown dead remains of plants and animals and decompose them into organic matter.

Valency of an element can be determined by its electronic configuration as follows:-

 (i) If Valence electron ≤ 4

  Then, Valency = Valence electrons

 (ii) If Valence electron > 4

  Valency = 8 –Valence electrons

 Valency of an element of atomic number 9(nine):-

 Electronic Configuration= 2, 7

 Here, Valence electron=1

 Valency= 8 – 7 = 1

Element X has atomic number 13

i.  Electronic configuration= 2,8,3

ii. Valence electrons of X= 3

Group number= 3+10=13

Group to which X belongs is 13

iii. X is a non-metal

iv. Electronic configuration of Br is 2,8,18,7

Valency of Br= 1

Electronic Configuration of X is 2,8,3

Valency of X= 3

Element X= Aluminium(Al)

Formula of its bromide is AlBr₃

The genetic difference between a sperm and an egg is that, a sperm contains either X or Y chromosome, while an egg always contains X chromosome. It is an essential factor for deciding the sex of a child as during fertilisation, an ovum fuses with a sperm carrying either an X chromosome or a Y chromosome. The zygote carrying XX chromosomes results in the formation of a girl child, while that carrying XY results in the formation of a boy child.

Advantages of vegetative reproduction practiced in case of an orange plant are:

1. It helps in the propagation of plants which have lost their ability to produce viable seeds.
2. Plants produced are genetically similar to the parent plant and have similar characteristics.

Four properties of the image formed by a plane mirror are given below:

1. Image formed by plane mirror is virtual.

2. Image formed by plane mirror is erect and laterally inverted.

3. Size of both the object and its image is always same.

4. Image distance and object distance remains same.

When a second identical prism ‘Q’, is placed in an inverted position in front of the white light spectrum from a prism ‘P’, then again recombination of the spectrum produces white light.