A cylinder containing an ideal gas is in vertical position and has a piston of mass M that is able to move up or down without friction (see figure). If the temperature is increased, then [NCERT Exemplar)

Consider the diagram, where an ideal gas is contained in a cylinder, having a piston of mass M. Friction is absent.

The pressure inside the gas will be p = p_a + Mg/A
where, p_a = atmospheric pressure,

            A = area of cross-section of the piston
and    Mg = weight of piston.
Hence, p = constant
As,      pV = nRT
$\Rightarrow$When temperature increases, volume (V) increases at constant pressure.