Concept:Spontaneity is determined by Gibbs free energy: ΔG=ΔH−TΔS. A reaction is spontaneous when ΔG<0.Explanation:For spontaneity, ΔH−TΔS<0, meaning ΔH<TΔS.Option C states that ΔH is positive but less than TΔS.So ΔH−TΔS<0, hence ΔG<0, which favours spontaneity.Answer:C. ΔH is positive and less than TΔS