Classify each reaction in as many ways as possible.
(a) NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(aq)
(b) 2 Rb(s) + Br2(g) → 2 RbBr(s)
(c) Zn(s) + NiBr2(aq) → Ni(s) + ZnBr2(aq)
(d) Ca(s) + 2 H2O(l) → Ca(OH)2(aq) + H2(g)
When one species knocks out another from its compound and takes its partner it's a single displacement reaction as in (3) and (4) above Zn replaces Ni, and Ca replaces H because H2O is in fact H-OH.
When partners are exchanged it is a double displacement...