Statistics

The probability distribution of a random variable $X$ is given below. Then, the standard deviation of $X$ is

$$ \begin{array}{llllll} \hline \boldsymbol{X}=\boldsymbol{x}_1 & 2 & 3 & 5 & 7 & 12 \\ \hline \boldsymbol{P}\left(\boldsymbol{X}=\boldsymbol{x}_1\right) & 3 k & k & k & 2 k & k \\ \hline \end{array} $$