The correct option is A 2√gR3
Applying energy conservation principle between the topmost point and the surface of earth, we have:
Loss in potential energy of the system = Increase in kinetic energy of the particle.
ΔU=ΔKE
mgh1+hR=12mv2
⇒mg(2R)1+2RR=12mv2
v=2√gR3
Hence, option (A) is the correct answer.