Question

Assertion : If dot product and cross product of $\vec{P}$ and $\vec{Q}$ are zero, it implies that one of the vector $\vec{P}$ and $\vec{Q}$ must be null vector.
Reason : A null vector is a vector of zero magnitude.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (B)

As per question, $\left|\vec{A} .\vec{B}\right|=\left|\vec{A}\times\vec{B}\right|=0$
This is possible if either A = 0 or B = 0.
Magnitude of a null vector is zero.