Mark against the correct answer in each of the following:

Mark $(\sqrt{)}$ against the correct answer in each of the following:

The unit vector normal to the plane containing $\overrightarrow{\mathrm{a}}=(\hat{\mathrm{i}}-\hat{\mathrm{j}}-\hat{\mathrm{k}})$ and $\overrightarrow{\mathrm{b}}=(\hat{\mathrm{i}}+\hat{\mathrm{j}}+\hat{\mathrm{k}})$ is 

A. $(\hat{\mathrm{j}}-\hat{\mathrm{k}})$

B. $(-\hat{j}+\hat{k})$

C. $\frac{1}{\sqrt{2}}(-\hat{\mathrm{j}}+\hat{\mathrm{k}})$

D. $\frac{1}{\sqrt{2}}(-\hat{\mathrm{i}}+\hat{\mathrm{k}})$