兩條chem的mc~中五level

D,D

For the 1st question, the question ask you that if the reaction can be reversed in Laboratory.
1)2Ca + O2 --->2CaO <-- Can be reversed only by Electrolysis of molten CaO, so its reverse reaction cannot be done in lab
2)2Hg+O2 ---->2HgO <-- reversed by heating
3)2Ag2O ---->4Ag(s) +O2 <-- reversed by heating
4)Na2CO3 + 10H2O ---->Na2CO3．10H2O <-- reversed by dehydration