A capacitor $0.1\;\mu F$ connected in series to a resistor of $10 \;M \; \Omega$ is charged to a certain potential and then made a discharge through the resistor. The time in which the potential will take to fall to half its original value is (Given $\log _{10}2=0.3010$):

Question

$$\begin {array} {1 1} (1)\;2 \;sec & \quad (2)\;0.693\;sec \\ (3)\;0.5 \;sec & \quad (4)\;1.0\;sec \end {array}$$