Write the chemical equation for the preparation of bleaching powder using chlorine gas with conditions.
a) Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
b) Ca(OCl)2 + Cl₂ → CaCl₂ + H₂O
c) CaCO₃ + Cl₂ → Ca(OCl)2 + CO₂
d) Ca(OH)₂ + Cl₂ → CaCl₂ + H₂O