Which of the following is a possible application of an $RC$ circuit?

$A$ circuit element is placed in a closed box. At time $t=0$,a constant current generator supplying a current of $1\, A$ is connected across the box. The potential difference across the box varies according to the graph shown in the figure. The element in the box is:

Find $I_1$ and $I_2$ at steady state.

Assertion : $A$ capacitor blocks direct current in the steady state.
Reason : The capacitive reactance of the capacitor is inversely proportional to frequency $f$ of the source of $emf$.

The capacitor $C$ is initially without charge. $X$ is now joined to $Y$ for a long time,during which $H_1$ heat is produced in the resistance $R$. The $X-Y$ connection is removed and $X$ is now joined to $Z$ for a long time,during which heat $H_2$ is produced in $R$.

$A$ capacitor is connected to a cell of $emf$ $E$ having some internal resistance $r$. The potential difference across the