The unit vectors along the mutually perpendicular x,y and z axes are $\hat{i},\;\hat{j}\; and \;\hat{k}$ respectively. Consider the plane $z=0$ and two vectors $\overrightarrow{a} and\;\overrightarrow{b}$ on that plane such that $\overrightarrow{a}\neq \alpha \overrightarrow{b}$ for any scalar $\alpha$. A vector perpendicular to both $\overrightarrow{a} and\;\overrightarrow{b}$ is ___________
- $\hat{k}$
- $\hat{i}-\hat{j}$
- $-\hat{j}$
- $\hat{i}$