on mercuration- demercuration produces the major product:

Alkene on oxymercuration - demercuration produces an alcohol in which the net reaction is the addition of ${\mathrm{H}}_2\mathrm{O}$ to the double bond in accordance with Markovnikov’s rule (i.e. -OH group adds to carbon containing lesser number of hydrogens). Hence, we have

Therefore, the choice (a) is correct