Answer:
The total number of molecules taking pert in the given reaction is 3.
Step-by-step explanation:
There are two reactant molecules participating in the given reaction
Mg+2HCL=MgCl2+H2
Here 1 molecule of magnesium(Mg) and 2 molecules of Hydrochloric acid(HCl) undergoing chemical reaction to generate magnesium chloride(MgCl2) and hydrogen gas(H2).
As a result the molecularity of the reaction is 3.