At what distance from the centre of a uniformly charged ring, maximum value of electric field will be obtained?

The correct option is B $5\text{m}$
Given:
$\lambda =+30\text{nC/m};R=5\sqrt{2}\text{m}$

We know that, maximum value of electric field for a ring of uniformly distributed charge over its circumference will be at

$\text{OP}=r=\frac{R}{\sqrt{2}}$

$\Rightarrow \text{OP}=r=5\text{m}$

Hence, $\left(b\right)$ is correct option.