Given $n$ real numbers $a_{1}, a_{2}, \ldots a_{n}$, the value of $x$ for which sum of the square of all the deviations is least is
(a) $a_{1}+a_{2}+\ldots+a_{n}$
(b) $2\left(a_{1}+a_{2}+\ldots+\sigma_{n}\right)$
(c) $a_{1}^{2}+a_{2}^{2}+\ldots+a_{n}^{2}$
(d) $\frac{a_{1}+a_{2}+\ldots+a_{n}}{n}$