An uncharged metal object M is insulated from its surroundings. A positively charged metal sphere S is then brought near to M. Which diagram best illustrates the resultant distributions of charge on S and M ?

Negative charges are attracted to surface of M near S by electrostatic induction and positive charges are repelled to surface of M away from S such that entire M still remains neutral (uncharged). 
Charge on S is also redistributed to have more charge on surface near to M due to the field set up by negative charges on M. Diagram b, thus, best illustrates the charge distribution on both S and M.