Joule – Thomson coefficient is the ratio of
(a) Pressure change to temperature change occurring when a gas undergoes the process of adiabatic throttling
(b) Temperature change to ressure change occurring when a gas undergoes the process of adiabacti throttling
(c) Temperature change to pressure change occurring when a gas undergoes at the process of adiabatic compression
(d) Pressure change to temperature change occurring when a gas undergoes the process of adiabatic compression