In a rigid body in plane motion, the point R is accelerating with respect to point P at $10 \angle 180^{\circ} \: m/s^2$. If the instantaneous acceleration of point $Q$ is zero, the acceleration (in $m/s^2$) of point $R$ is

1. $8 \angle 233^{\circ}$
2. $10 \angle 225^{\circ}$
3. $10 \angle 217^{\circ}$
4. $8 \angle 217^{\circ}$