In desert areas, the water vapor content is

Nitrogen is obtained from the fractional distillation of liquefied air at about

A. 196°C

B. 186°C

C. 176°C

D. 166°C

A greenhouse gas that absorbs energy and maintains the earth's temperature is

A. carbon dioxide

B. oxygen

C. nitrogen

D. argon

The main constituent in air is

A. nitrogen

B. oxygen

C. argon

D. water vapor

On cooling, a liquid will be changed into

A. dense

B. solid

C. semi-solid

D. liquid

Combustion cannot take place without

A. water

B. carbon

C. air

D. zinc