Correct option is (b) L/D<3/4
Explanation: By principle of buoyancy,
Weight of cylinder = Weight of water displaced
h=2L/3
AG=L/2
AB=L/3
BG=AG-AB=L/6
GM= Metacentric height=I/∀ – BG=3D2/32L-L/6
For stable equilibrium, GM should be positive
GM>0
i.e L/D<3/4.