Science: 2012: CBSE: [Delhi]: Set – III

The first member of the series of carbon compounds having –COOH group is Methanoic acid

Crystalline lens: It provides the finer adjustment of focal length required to focusobjects at different distances on the retina.

Ozone layer is responsible for the absorption of harmful Ultraviolet B radiations, which are emitted by the sun. Without the presence of ozone layer at the higher level of atmosphere, more of the sun’s ultraviolet radiations would penetrate the atmosphere and reach the surface of the earth.

According to Ten Percent Law of Energy, only 10% energy is transferred from one trophic level to another. Thus, if 1000 J of solar energy is available to the grass, only 100 joules of energy would be available to the deer to transfer it to the lion.

(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.

Atomic number of element=13

        Electronic configuration= 2,8,3

(a) According to electronic configuration, it belongs to 13^th group and 3^rd period

Number of valence electrons=3

Since number of valence electrons are more than 2 so group number=10+3=13

Valence electrons belongs to M shell so period number is 3

(b) The element is Aluminium as its atomic number is 13 and it is a metal.

Advantages of vegetative propagation in plants are:

• It is an easy, rapid and cheapest method of propagating plants in large numbers.
• It helps in producing genetically identical plants.
• It helps in producing superior quality flowers.
• It is useful in plants that are unable to produce viable seeds.

Of the given list, banana and rose can be raised by vegetative propagation.

Seminal vesicles, prostate gland, testes and bulbourethral glands are the parts of human male reproductive system which contribute fluid to the semen. Following are the advantages semen offer to the sperm:

• It provides nourishment to the sperm.
• It helps in transportation of the sperm.

(i) Ray of light travelling parallel to the principal axis, after refraction through convex lens, passes through focus.

(ii) Ray of light passing through the optical centre of a convex lens passes undeviated.

(iii)Ray diagram when object is between f₁ and 2f₁of a convex lens:

 

Ray diagram to show the formation of a rainbow

Rainbow is caused by dispersion of sunlight bytiny water droplets, present in the atmosphere.These water droplets refract and dispersethe incident sunlight, then reflect it internally, after that when it comes out of the raindropthese droplets finally refractit again. Due to thedispersion of light and internal reflection, different colours reachthe observer’s eye.