Q.A vector whose initial and terminal points coincide, is called ________.

Zero Vector

The zero vector, written $\vec{0}$, is the vector whose initial and terminal points coincide. Because it starts and ends at the same place, it has magnitude $|\vec 0| = 0$ and no definite direction; for this reason it is also called the null vector. In component form it is $\vec 0 = 0\hat i + 0\hat j + 0\hat k$, that is, $(0, 0, 0)$.

Despite having no direction, the zero vector plays an essential structural role. It is the additive identity for vectors: for every vector $\vec a$,

Multiplying any vector by the scalar $0$ produces $\vec 0$, and multiplying $\vec 0$ by any scalar leaves it unchanged. It is conventionally taken to be parallel to every vector. Its dot product with any vector is $0$, and its cross product with any vector is again $\vec 0$. …