Answer:
Option C
Explanation:
$\because(\vec{a}\times\vec{b})\times\vec{a}=(\vec{a}.\vec{a})\vec{b}-(\vec{a}.\vec{b})\vec{a}$
$\therefore(\hat{j}-\hat{k})\times(\hat{i}+\hat{j}+k)=(\sqrt{3})^{2}(\vec{b})-(\hat{i}+\hat{j}+k)$
$\Rightarrow 3\hat{b}=3\hat{i}\Rightarrow \hat{b}=\hat{i}$