The time constant for the given RC circuit where$ R = 1 K\Omega$ and C = 103 pF will be

2 mili second    $ 1 \mu second$   1.5 mili second     0.5 mili second.

$ 1 \mu second$

$ \tau = RC = 10^3\times 10^3\times 10^{-12} Sec = 1\mu Second$