(A) : The molecular mass of acetic acid in benzene is more than the actual value of the solute.
(R) : Molecules of acetic acid dimerize in benzene due to hydrogen bonding.

Explanation: Due to hydrogen bonds between its molecules, acetic acid (molar mass 60 g/mol) dimerizes in benzene, causing the molecular weight to double from its initial value.
As a result, the molecular weight of benzene acetic acid is 120 g/mo.
Therefore, the correct option is (A) Both (A) and (R) are true and (R) is the correct explanation of (A).