Ans=A

The magnitude of any vector can be found by taking the square root of sum of the squares of its two components.

$\left| \overrightarrow{r} \right|=\sqrt{a^{2}+b^{2}}$

$\left| \overrightarrow{r} \right|=\sqrt{4^{2}+3^{2}}$

$\sqrt{25}$=5

Hence, the answer is 5.