Question

Which of the following reactions obeys the Law of Conservation of Atoms?

H2O → H2 + O2
CuSO4 + Zn → ZnCl2 + Cu
Zn + HCl → ZnCl2 + H2
PbCl2 + Al → AlCl3 + Pb
Zn + 2HCl → H2 + ZnCl2

Answer 1

None Do. These are all skeleton equations that must first be balances by adding coeffecients.
Also, CuSO4 + Zn -> ZnCl2 + Cu has different products in terms of elements than its reactants...

Answer 2

Zn + 2HCl → H2 + ZnCl2 obeys the Law of Conservation of Atoms.

On each side of the arrow there are 1 Zn atom, 2 H atoms, and 2 Cl atoms.

Thus, all atoms are conserved.