In a $RC$ circuit, where $R$ is resistance and $C$ is capacitance, which of the following has the dimension of time?

In the given figure,initially the capacitor is uncharged. The ratio of current at $t = 0$ and $t = \infty$ will be:

During charging and discharging of a capacitor:

Given,
${R_1} = 1\,\Omega, R_2 = 2\,\Omega$
${C_1} = 2\,\mu F, C_2 = 4\,\mu F$
The time constants (in $\mu s$) for the circuits $I, II, III$ are respectively:

$A$ $4 \mu F$ capacitor and a resistance of $2.5 \, M\Omega$ are in series with a $12 \, V$ battery. Find the time after which the potential difference across the capacitor is $3$ times the potential difference across the resistor. (Given $\ln(2) = 0.693$)

The switch $S$ shown in the figure is kept closed for a long time and then opened at $t = 0$. The current in the middle $20\, \Omega$ resistor at $t = 0.25\, ms$ is: