Question

Identify the correct statements from the following: I. Group 15 elements form electron rich hydrides II. Density of heavy water is higher than that of water III. Water containing soluble salts of magnesium and calcium is called soft water

• A. I, II, III
• B. I, III only
• C. II, III only
• D. I, II only

Hint:

Hard water contains dissolved calcium and magnesium salts, whereas soft water forms lather readily with soap.

Answer 1

The Correct Option is D

Concept: Group 15 hydrides contain a lone pair of electrons and hence are electron-rich. Heavy water (\(D_2O\)) has a greater density than ordinary water (\(H_2O\)). Water containing dissolved calcium and magnesium salts is called hard water.

Step 1: Examine Statement I.
Hydrides of Group 15 elements are: \[ NH_3,\; PH_3,\; AsH_3,\; SbH_3 \] All these molecules possess a lone pair of electrons on the central atom. Hence they are electron-rich hydrides. Therefore, \[ \boxed{\text{Statement I is correct}} \]

Step 2: Examine Statement II.
Heavy water contains deuterium instead of hydrogen. \[ D_2O \] Density of heavy water: \[ 1.105\,g\,cm^{-3} \] Density of ordinary water: \[ 1.0\,g\,cm^{-3} \] Therefore, \[ \boxed{\text{Statement II is correct}} \]

Step 3: Examine Statement III.
Water containing dissolved salts of calcium and magnesium is known as hard water. Such water does not form lather easily with soap. Hence, \[ \boxed{\text{Statement III is incorrect}} \] Thus, only statements I and II are correct. \[ \boxed{\text{I, II only}} \]