Adiabatic process is a process in which _ is constant (a) temperature (b)volume (c)pressure (d) heat

Adiabatic process is a process in which heat is constant

Explanation:

The processes in which temperature remains constant is called isothermal process.

The process in which Volume remains constant is called isochoric process.  

The process in which pressure remains constant is called isobaric process.

 The process in which no heat is gained or lost by the system, Hence heat remains constant is called as adiabatic process.

Thus option d) heat is correct