In which of the processes does the internal energy of the system remain constant?

Which of the following is a slow process?

$A$ container that suits the occurrence of an isothermal process should be made of

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

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: