Which of the following,in general,is a slow process?

The condition $dQ = dW$ holds good in which of the following?

$A$ thermodynamic process in which the temperature $T$ of the system remains constant,although other variables $P$ and $V$ may change,is called:

$A$ certain gas is isothermally compressed to $(1/3)^{rd}$ of its initial volume $(V_0 = 3 \ \text{L})$ by applying required pressure. If the bulk modulus of the gas is $3 \times 10^5 \ \text{N/m}^2$,the magnitude of work done on the gas is . . . . . . $J$.

$Assertion :$ In an isothermal process,the whole of the heat supplied to the body is converted into internal energy.
$Reason :$ According to the first law of thermodynamics,$\Delta Q = \Delta U + P\Delta V$.

$A$ gas undergoes a change at constant temperature. Which of the following quantities remain fixed?