Correct Answer - C
At the instant block is in equilibrium position its speed is maximum and compression in spring is x given by
`kx=mg` (i)
From conservation energy,
`mg(L+x)=(1)/(2)kx^2+(1)/(2)mv_(max)^2` .(ii) From Eqs (i) and (ii) we get `v_(max)=(3)/(2)sqrt(gL)`