C-07-Q110mediumsingle_mcq2HCl+Mg(OH)2→MgCl2+?\mathrm{2HCl + Mg(OH)_2 \to MgCl_2 + ?}2HCl+Mg(OH)2→MgCl2+? — the missing product is—aCO2\mathrm{CO_2}CO2b2H2O\mathrm{2H_2O}2H2