Entropy of a substance remains constant during a/an __________ change.

Solution (By Examveda Team)

Since only for a reversible process we have relation :
$$TdS = \delta Q$$
Since for an adiabatic process $$\delta Q = 0$$ $$ \,\,\, \Rightarrow $$ for an reversible adiabatic process $$TdS = 0.$$
So, entropy remains constant. Whereas for an irreversible adiabatic process $$TdS \geqslant 0.$$
Hence entropy goes on increasing for an irreversible adiabatic process.