When gases are heated from 20 to 40°C at constant pressure, their volumes

According to ideal gas equation

 PV = nRT

Pressure is constant.

Then volume is directly proportional to temperature

$\frac{{\mathrm{V}}_1}{{\mathrm{V}}_2}=\frac{{\mathrm{T}}_1}{{\mathrm{T}}_2}$

${\mathrm{V}}_2=\frac{{\mathrm{T}}_1}{{\mathrm{T}}_2}{\mathrm{V}}_1$

${\mathrm{V}}_2=\frac{313}{293}{\mathrm{V}}_1$

Different gases increase by different amounts when heated through the same amount of temperature. It increases but to a different extent.

Therefore, the correct option is D.