Answer
1. $2H_{2} + O_{2} \rightarrow 2H_{2}O$ : Synthesis Reaction
2. $MgCl_{2} \rightarrow Mg^{2+}+Cl_{2}$ : Decomposition Reaction
3. $Zn^{2+} + CuCl_{2} \rightarrow ZnCl_{2} + Cu^{2+}$ : Exchange Reaction
4. $Li_{2}CO_{3} \rightarrow Li_{2}O+CO_{2}$ : Decomposition Reaction
Work Step by Step
In synthesis reaction molecules of two element combine to form a new molecular compound like in first reaction.
In decomposition reaction one molecule decays into other molecules like in second and fourth reaction.
In exchange reaction one atom of a compound is replaced by another atom like in third reaction.
