Mark against the correct answer in each of the following:

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

If $\overrightarrow{\mathrm{a}}=(2 \hat{\mathrm{i}}+4 \hat{\mathrm{j}}-\hat{\mathrm{k}})$ and $\overrightarrow{\mathrm{b}}=(3 \hat{\mathrm{i}}-2 \hat{\mathrm{j}}+\lambda \hat{\mathrm{k}})$ be such that $\vec{a} \perp \vec{b}$ then $\boldsymbol{\lambda}=$ ? 

A. 2

B. $-2$

C. 3

D. $-3$