1. **Problem statement:** Find the angle on the unit circle corresponding to point $A(-1,0)$. 2. **Recall:** On the unit circle, the coordinates of a point are $(\cos \theta, \sin \theta)$ where $\theta$ is the angle measured from the positive x-axis. 3. **Given:** Point $A$ has coordinates $(-1,0)$. This means $\cos \theta = -1$ and $\sin \theta = 0$. 4. **Find angle:** The cosine of $\pi$ radians (or 180°) is $-1$ and sine is $0$. So, the angle corresponding to $A$ is $\pi$. 5. **Answer:** The angle is $\pi$. Therefore, the correct choice is (B) $\pi$.