Which of the following is applicable for isothermal process?

For an isothermal process, the temperature of the system remains constant, which means $\Delta T = 0$.

For an ideal gas, the change in internal energy is given by $\Delta U = nC_v\Delta T$. Since $\Delta T = 0$, the change in internal energy is zero, so $\Delta U = 0$.

According to the first law of thermodynamics:
$\Delta U = Q + W$

Substituting $\Delta U = 0$ into the equation, we get:
$0 = Q + W$

$W = -Q$

This indicates that the work done on the system is equal to the negative of the heat absorbed by the system.

Answer: $W=-Q$