If mass of earth is M, radius is R and gravitational constant is G, then work done to take 1 kg mass from earth surface to infinity will be :

√GM/2R GM/R √2GM/R GM/2R

GM/R

Work done = \(U_{final} - U_{initial}\)   = \(U_{\infty} - U_R\)   = \(0 - (\frac{-GMm}{R})\)     =\(\frac{GMm}{R}\)   = \(\frac{GM}{R}\) ... [As mass m = 1 kg]