Which equation describes a single-replacement reaction?

Responses

H2 (g) + Br2 (g)→2HBr (g)
Mg(s)+Cu(NO3)2(l)→Mg(NO3)2(s)+Cu(s)
2N2O5 (g)→O2 (g) + 4NO2 (g)
2Na(s) +Cl2(g) → 2NaCl(s)