Regarding the assertion and reason; choose the correct option.
Assertion (A): In case of acute constipation, purgatives containing magnesium salts are usually used to alleviate it
Reason (R): The osmotic effect of Mg2+ in the intestinal lumen prevents water from being reabsorbed from the intestine. Mg2+ increases the solute concentration in the intestinal lumen because Mg2+ is absorbed very slowly