A particle is projected with a velocity \( \sqrt{\frac{4 g R}{3}} \) vertically upward from the surface of the earth, \( R \) being the radius of the earth \& \( g \) being the acceleration due to gravity on the surface of the earth. The velocity of the particle when it is at half the maximum height reached by it is
(A) \( \sqrt{\frac{g R}{2}} \)
(B) \( \sqrt{\frac{g R}{3}} \)
(C) \( \sqrt{g R} \)
(D) \( \sqrt{\frac{2 g R}{3}} \)