If $\overrightarrow{a},\overrightarrow{b},\overrightarrow{c}$ are a right handed triad of mutually perpendicular vectors of magnitude $a, b , c$ than value of $[\overrightarrow{a} \overrightarrow{b} \overrightarrow{c}]$ is

Question

$$\begin{array}{1 1}(1) a^{2} b^{2} c^{2} &(2)0\\(3)\frac{1}{2} abc&(4)abc \end{array}$$