Which equation shows conservation of mass? a.  h2o → h2 + o2 b.  pcl5 → pcl3 + cl2 c.  na + cl2 → nacl d.  al + br2 → albr3

B. PCl₅ → PCl₃ + Cl₂.

Explanation:

H₂O → H₂ + O₂, the oxygen has 1 atom in the reactants side while has 2 atoms in the products side.

to be balanced and apply conservation of the mass it should be: H₂O → H₂ + 1/2O₂.

The number of atoms of P (1 atom) and Cl (5 atoms) are the same in both sides of reactants and products.

Na + Cl₂ → NaCl, the Cl has 2 atoms in the in the reactants side while has 1 atom in the products side.

to be balanced and apply conservation of the mass it should be: Na + 1/2Cl₂ → NaCl.

Al + Br₂ → AlBr₃, the Br has 2 atoms in the in the reactants side while has 3 atoms in the products side.

to be balanced and apply conservation of the mass it should be: 2Al + 3Br₂ → 2AlBr₃.

it's all four options.