Step 1: Concept The component of vector $\vec{A}$ in the direction of $\vec{B}$ is given by $A \cos \theta$, where $\theta$ is the angle between them.
Step 2: Meaning If the component is zero, then $A \cos \theta = 0$. Since the magnitude $A$ is non-zero, $\cos \theta$ must be zero.
Step 3: Analysis The cosine of an angle is zero when the angle $\theta = 90^{\circ}$.
Step 4: Conclusion An angle of $90^{\circ}$ means that the two vectors are perpendicular to each other.
Final Answer: (B)