The correct option is C 3j−k¯¯¯¯¯¯10
As we know, a vector caplanar to a, b and
orthogonalto c is λ{(a×b)×c}.
∴ A vector coplanar to (2i+j+k),(i−j+k)
and orthogonal to (3i+2j+6k).
=λ[{2i+j+k)×(i−j+k)}×(3i+2j+6k)]
=λ−21j+7k
∴ A unit vector is ±a×b×ca×b×c
=±−21j+7k−212+72=±3j−k¯¯¯¯¯¯10