Science [2 Mark Questions]

CFCs, i.e. chlorofluorocarbons are used in fire extinguishers it is most common ozone depletion substance (ODS), which create a hole in ozozne layer thus allowing UV radiations from the Sun to enter into the atmosphere.

The two laws of refraction are:
i. The incident ray, the refracted ray and the normal at the point of incidence, all lie in the same plane.
ii. The ratio of the sine of the angle of incidence (i) to the sine of angle of refraction (r) is a constant for the pair of given media.
This constant is called the refractive index of the second medium with respect to the first medium,

In Humans blood flow in two directions simultaneously in one cardiac cycle. Oxygenated blood comes to the heart from the lungs and at the same time, de-oxygenated blood goes from Heart towards the lungs. Because of this double movement is blood circulation in the human heart called double circulation.

After fertilization, the zygote starts dividing by repeated mitotic divisions called cleavage. In about 4 to 5 days after fertilization, zygote becomes a multicellular structure called blastocyst. The blasto cyst gets attached to the lining of uterus is called implantation.

i. Carbon forms large no. of compounds due to the following reasons:
Catenation: The property of an element to combine with itself to form long chain is called catenation. Atoms of same element combine through covalent bonds and form long chains and structures. Carbon exhibit this property of catenation. Due to which we see such a large variety of organic compounds in nature.
Tetravalency: Carbon has a valency of four. So, it is capable of bonding with four other atoms of carbon or atoms of some other element. Compounds of carbon are formed with oxygen, nitrogen, hydrogen, sulphur, chlorine and many other elements, which may act as functional groups with specific properties which depend on the elements other than the carbon present in the molecule.
ii. Some compounds are called saturated because they contain single bond only between two carbon atoms but some are
unsaturated because in these hydrocarbons, valence of carbon is satisfied by double or triple bond.
iii. Unsaturated hydrocarbons are more reactive because of the presence of double and triple bonds between them, which are weaker compared to single bond.