Picture the cyclone as a spinning vortex. The particle needs a strong outward push, which comes from a high tangential velocity generating centrifugal force much greater than gravity.
\[F_c = \frac{m v_t^2}{r}\]
The higher \(v_t\) is, the stronger this outward push, so a good design maximises tangential velocity.
But the air also drifts inward toward the exit pipe at the radial velocity \(v_r\). If \(v_r\) is too high, particles are carried to the exit before centrifugal force can push them to the wall. So the design also keeps \(v_r\) small, giving particles time to separate.
\[\boxed{\text{High tangential velocity and low radial velocity, option 2}}\]