The distribution of phase angle between identical zero mean Gaussian random signals?
$$\mathcal{X_1}=\mathcal{N}(0,\sigma^2)$$
$$\mathcal{X_2}=\mathcal{N}(0,\sigma^2)$$
$$\theta=\arctan(\mathcal{X_1},\mathcal{X_2})$$

Since arctan ranges from \$-\frac{\pi}{2}\$ to \$-\frac{\pi}{2}\$

there can only be one answer and that is c, you could do the math but the answer is c

These questions are designed to be tricky, simple relationships can save you time if you look at the question as a whole. In this case you need to know what the output of arctan is.