Which of these is a unit vector?

Explanation

1. 01

   A unit vector has magnitude 1.

2. 02

   $\lvert 2\hat{i} + 3\hat{j} - 6\hat{k} \rvert = \sqrt{4 + 9 + 36} = 7$, so $\frac{1}{7}(2\hat{i} + 3\hat{j} - 6\hat{k})$ has magnitude 1; the others have magnitudes $\frac{1}{\sqrt{3}}$, $\sqrt{\frac{3}{2}}$ and $\sqrt{2}$.