Right answer is (b) Associative law for cross product: (PxQ)xS ≠ Px(QxS)
Explanation: The associative law is defined in the cross product of three vectors. This property is though valid for the dot product. But for the cross product, it is not true. It is because, in the dot product the final result is the scalar quantity, but in a cross product it is the direction too. Thus the answer.