The process which is accompanied with decrease in entropy is

CaO(s)+CO2(g)→∆CaCO3s ;Number of gaseous moles decreases during the process thus randomness decreases.∴∆S=-ve;1….H2Ol→H2Og ...∆S=+ve;2…N2g+O2g→2NOg ...∆S=0;4…H2Ol→H2g+12O2g...∆S=+ve;