For the given reaction. CaO(s)+CO2(g)→CaCO3(s) At low temperature, the value of Δn=0−1=(−)1 ∵Δn= moles of gaseous products − moles of gaseous reactants For the reaction contain gaseous species. ΔH=ΔE+ΔnRT where, ΔH= enthalpy change ΔE= internal energy change Δn= change in number of moles R= gas constant T= temperature in Kelvin. ∵ Δn=(−)1 ΔH=ΔE−RT means ΔH<ΔE (negative) and of exothermic nature. For the reaction to occur spontaneously, ΔG=ΔH−TΔS, value of ΔG must be negative. At low temperature for ΔG and ΔH to be negative. ∵Δn=(−)1 So, ΔS must be negative, as number of gaseous moles in product side are less than of reactant side. Hence, the correct set is ΔH= negative ΔS= negative ΔG= negative ∴(b) is the correct option.