= Solution
In <water>, separated <benzene> <molecules> require separate hydration environments around nonpolar surface. Bringing them together buries part of that surface and reorganizes the surrounding <water>. The resulting <solvent> contribution favours association relative to <cyclohexane>, where <benzene> was already well solvated by dispersion. \b[This <solvent>-mediated contribution is the <hydrophobic effect>], not formation of a new <covalent bond> or a claim that <benzene> has become a conventional <hydrogen>-bond acceptor like <oxygen>.
The supplied constants imply a thirtyfold enhancement. With matched <standard states>,
$$
\Delta\Delta G^\circ=-RT\ln(0.9/0.03)=-RT\ln30\simeq\boxed{-8.43\ \mathrm{kJ\,mol^{-1}}}
$$
at an illustrative 298 K. The <water> value is still slightly below $1\ \mathrm{M^{-1}}$, so enhancement relative to <cyclohexane> does not mean a negative standard association free energy for a 1 M <standard state>, nor does it imply that dilute <benzene> is all dimer. No universal “<entropy> only” explanation is needed: <solvent> <enthalpy> and <entropy> both contribute and depend on <temperature>.
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