Explanation

(b)
Let two vectors are $\overrightarrow{\mathbf{a}}\ and\ \overrightarrow{\mathbf{b}}$
Given, $|\overrightarrow{\mathbf{a}} \times \overrightarrow{\mathbf{b}}|$=$\sqrt{3}|\overrightarrow{\mathbf{a}} \bullet \overrightarrow{\mathbf{b}}|$
$\Longrightarrow |\overrightarrow{\mathbf{a}}| \bullet |\overrightarrow{\mathbf{b}}|\ sin$ θ=$\sqrt{3}\ |\overrightarrow{\mathbf{a}}||\overrightarrow{\mathbf{b}}|$cos θ
$\Longrightarrow \tan\theta = \sqrt{3}$
$\Longrightarrow \ \theta = \frac{\pi}{3}$