The balanced chemical equation for the reaction is as follows
Mg(OH)₂ + 2HCl ---> MgCl₂ + 2H₂O
molar ratio of HCl to MgCl₂ is 2:1
There's excess Mg(OH)₂ therefore HCl is the limiting reactant.
the amount of product formed is determined by the amount of limiting reactant present
so when 2 mol of HCl reacts - 1 mol of MgCl₂ is produced
therefore when 4.66 mol of HCl reacts - 1/2 x 4.66 = 2.33 mol of MgCl₂ is produced
answer is 2.33 mol of MgCl₂
