Questions in vectors-m

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	If $\mathbf{a}=\mathbf{i}-\mathbf{j},\mathbf{b}=\mathbf{i}+\mathbf{j},\,\,\,\mathbf{c}=\mathbf{i}+3\mathbf{j}+5\mathbf{k}$and$\mathbf{n}$is a unit vector such that $\mathbf{b}.\mathbf{n}=0,\mathbf{a}.\mathbf{n}=0$then the value of $\|\mathbf{c}\ .\ \mathbf{n}\|$ is equal to
	A unit vector perpendicular to the plane containing the vectors $\mathbf{i}-\mathbf{j}+\mathbf{k}$ and $-\mathbf{i}+\mathbf{j}+\mathbf{k}$ is