a)Ca + 2H2O --> Ca(OH)2 + H2
metal + water = metal oxide/hydroxide + hydrogen (hydroxide in this case)
water is oxidising agent i.e. it gets reduced, Ca is oxidised and gains OH i.e. becomes basic. OH has 2 because Ca ion has 2+, and OH is 1-
b)CaCO3 + 2HCl --> CaCl2 + CO2 + H2O
carbonate +...