[Maximum number: 1]

Air is a mixture of gases.
The melting and boiling points of some gases present in clean, dry air are shown.
In the fractional distillation of liquid air, which gas boils first?

gas

melting point $/{ }^{\circ} \mathrm{C}$

boiling point $/{ }^{\circ} \mathrm{C}$

argon

-189

-186

krypton

-157

-153

nitrogen

-210

-196

oxygen

-219

-183

[Maximum number: 1]

Which processes do not produce carbon dioxide?
1 heating limestone
2 burning gasoline in car engines
3 photosynthesis
4 production of nylon

1 and 2

1 and 3

2 and 4

3 and 4

[Maximum number: 1]

Which pollutant gas is produced by the decomposition of vegetation?

carbon monoxide

methane

nitrogen dioxide

sulfur dioxide