The unit vector perpendicular to each of $2 \hat {i}-\hat {j}+\hat {k}$ and $ 3 \hat {i}+4 \hat j-\hat k$ is :

Question

\[(a)\;\frac{(-3,5,11)}{155} \quad (b)\;\frac{(-3,5,11)}{\sqrt {155}} \quad (c)\;\frac{(3,5,11)}{\sqrt {155}} \quad (d)\;\frac{(3,-5,11)}{\sqrt {155}}\]