The mean-square of a zero-mean random process is $\frac{kT}{c},$ where $k$ is Boltzmann’s constant, $T$ is the absolute temperature, and $C$ is a capacitance. The standard deviation of the random process is
1. $\frac{kT}{c} \\$
2. $\sqrt{\frac{kT}{c}} \\$
3. $\frac{c}{kT} \\$
4. $\frac{\sqrt{kT}}{c}$