Which of the following substances combines with Magnesium to give a laxative affect to the water ?

• A. Magnesium
• B. Sulphates
• C. Chlorides
• D. Nitrates

Answer: (B)

The key idea here is saline laxatives— salts that draw water into the colon to soften stool and stimulate bowel movement. When magnesium pairs with sulfate, it forms magnesium sulfate, a well-known saline laxative. The magnesium ion isn’t fully absorbed, and the sulfate contributes to the osmotic effect, pulling water into the intestinal lumen. This increased water in the stool makes it softer and speeds up peristalsis, producing the laxative effect. Magnesium chloride or magnesium nitrate aren’t the standard salts used for this purpose, so the combination with sulfates best explains the laxative action. Therefore, sulfates is the correct choice.