The direction of conventional current is opposite to the direction of flow of
electrons
Explanation for correct answer
Electrons flow from a point where there is excess amount of electrons to a point of deficit.
By convention the direction of electric current is taken to be from positive terminal of the battery along the wire to the negative terminal.
The direction of conventional current is taken to be the opposite to the direction of flow of electrons.
Hence option (a) is the correct answer
Explanations for incorrect answer
It is said that direction of conventional current is taken to be the opposite to the direction of electrons alone and not for protons or neutrons
Hence option (b),(c) are incorrect answers