During which thermodynamic process does $T$ remain constant, while the other two variables $P$ and $V$ change?

$A$ vertical cylinder with heat-conducting walls is closed at the bottom and is fitted with a smooth light piston. It contains one mole of an ideal gas. The temperature of the gas is always equal to the surrounding's temperature,$T_0$. The piston is moved up slowly to increase the volume of the gas to $\eta$ times. Which of the following is incorrect?

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

Is the melting of ice an adiabatic or an isothermal process?

$Assertion :$ The isothermal curves intersect each other at a certain point.
$Reason :$ The isothermal change takes place slowly,so,the isothermal curves have very little slope.

What is the value of the specific heat of a gas during an isothermal process?