Four iron rings P, Q, R, S having the same density, but different radius, P = 5r/2, Q = 2r, R = 7r/4, S = 3r sinks in the honey. Which one of the order is correct starting from reaching first at bottom of the surface?
1. R, P, Q, S
2. R, Q, P, S
3. S, P, Q, R
4. S, Q, P, R