Correct Answer - B
The angular frequency of simple harmonic motion is given by, `omega = sqrt((k)/(m))`
The velocity of block, when it at a displacement of `y`from mean position is given by, `v = omega sqrt(A^(2) -y^(2))` , where `A` is the amplitude of oscillation. For given initial condition,
`v_(0) = sqrt((k)/(m)) sqrt(A^(2) - h^(2)) rArr A^(2) = (mv_(0)^(2))/(k) +h^(2)`
`rArr A = sqrt((mv_(0)^(2))/(k)+h)`