Answer: The correct option is a) & d)
Given in question $|\vec{A}+\vec{B}|=|\vec{A}-\vec{B}|$, it can be assertive when $| A |=0$ or $| B |=0$ or both are zero.
The provided statement can also be true if both requirements are met at the same time, which is what is meant by
Therefore we can write,
This implies,
This gives the always true condition that is when $A$ is perpendicular to $B$.