Correct option is A. 0.25 N
In the given problem at the extreme position, the tension in the string and the weight mg balance each other.
But weight mg is resolved into $$mgcos\theta$$ and hence
$$T = mgcos\theta = \left(50 \times 10^{-3}\right) \times (10) \times \frac{1}{2}=0.25 N$$