Questions

A greenhouse gas is a gas in an atmosphere that absorbs and emits radiant energy within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. 

Carbon dioxide is a main greenhouse gas, found in car exhaust pipes.
Methane and nitrous oxide is another type of greenhouse gas.

Oxygen is the only clean gas out there because we need it to survive. Therefore, the only gas that is not a greenhouse gas is Oxygen.

The Periyar Sanctuary covers an area of 777sq km. It was established in 1949. Elephants , Gaurs, leopards, solth bear, sambhars, barking deer, wild dogs, wild boars, black Nilgiri langur and water birds can be seen in this sanctuary.

Genetic drift or allelic drift is the change in the relative frequency in which a gene variant (allele) occurs in a population due to random sampling and chance.

When is genetic drift a major factor in evolution is

* When there is low gene flow.

* When there is no selective pressure.

* When there is a bottleneck.

Yes, a promise can be broken without being held.