A gas is contained in a metallic cylinder fitted with a piston. The gas is suddenly compressed by pushing the piston downward and is maintained at this position. After this process, as time passes the pressure of the gas in the cylinder

[Assume loss of heat to the surroundings]

As this is an adiabatic process, when the piston is suddenly pushed in, work is done on the gas, but it does not get enough time to reach equilibrium with its surroundings. In equilibrium it will be at the same temperature as surrounding which is lower than the temperature just before compression.

$\therefore$ as temperature decreases and volume is constant, pressure also decrease.