JEE Math Practice Question

Let xi (1 $$ \le $$ i $$ \le $$ 10) be ten observations of a random variable X. If $$\sum\limits_{i = 1}^{10} {\left( {{x_i} - p} \right)} = 3$$ and $$\sum\limits_{i = 1}^{10} {{{\left( {{x_i} - p} \right)}^2}} = 9$$ where 0 $$ \ne $$ p $$ \in $$ R, then the standard deviation of these observations is :

1. A.$${7 \over {10}}$$
2. B.$${9 \over {10}}$$
3. C.$${4 \over 5}$$
4. D.$$\sqrt {{3 \over 5}} $$