Give reason following the observations

Question

A-​​​​​The element carbon forms a very large number of compounds

B-​​​​​air holes of a gas burner have to be adjusted when the heated vessel get balanced by the flame

Answer 1

a) The element carbon forms a very large number of compounds. It's because, each 4 atoms of Carbon can form 4 different bonds. This is called catenation.
b) Air holes of a gas burner have to be adjusted when the heated vessels get blackened by the flame. It's because, Air holes is the place from where gas comes and and leads to burning of flame when these holes gets damaged then the passage of the gas gets blocked which in leads to inadequate burning leading to blackened vessel.

Answer 2

1.Reasons: Carbon forms a large number of compounds. Two properties of carbon that help it to form so many compounds is:
Catenation (The ability of carbon to combine with other atoms of carbon).
It forms strong covalent bonds with various elements like oxygen, nitrogen, chlorine, bromine, etc.

2.Blackening (deposition of unburnt carbon particles) of the cooking vessels show that incomplete combustion of the gas is taking place. As combustion is not taking place, the maximum amount of energy that can be obtained from the fuel cannot be obtained i.e., gas is being wasted. 

Limited supply of air results in the incomplete combustion of saturated hydrocarbons. Hence, the air holes of a gas burner have to be adjusted, so that, a sufficiently oxygen-rich mixture is burnt and a clean blue flame is obtained.