Given two vectors are $\hat{i} - \hat{j}$ and $\hat{i} + 2 \hat{j}$ the unit vector coplanar with the two vectors and perpendicular to first is :

Question

( A ) none of these
( B ) $\frac{1}{\sqrt{2}} ( \hat{i} + \hat{j} )$
( C ) $\pm \frac{1}{\sqrt{2}} ( \hat{i} + \hat{k} )$
( D ) $\frac{1}{\sqrt{5}} ( 2\hat{i} + \hat{j} )$