Question

Identify the sets in which both the metals react with water? \[ \text{I.}\quad Be,\ Mg \] \[ \text{II.}\quad Li,\ Mg \] \[ \text{III.}\quad Na,\ K \] \[ \text{IV.}\quad K,\ Ca \]

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

Hint:

Reaction with cold water: \[ K \gt Na \gt Ca \gt Mg \gt Be \] \[ Be \rightarrow \text{No reaction} \] \[ Mg \rightarrow \text{Reacts mainly with hot water/steam} \] \[ Na,\ K,\ Ca \rightarrow \text{React with water} \]

Answer 1

The Correct Option is C

Step 1: Examine Set I \((Be,\ Mg)\). Beryllium does not react with water because of its protective oxide film. \[ Be \; \text{does not react with water}. \] Magnesium reacts only with hot water or steam. Since both metals do not react readily with water, \[ \boxed{\text{Set I is incorrect}} \]

Step 2: Examine Set II \((Li,\ Mg)\). Lithium reacts with cold water. \[ 2Li+2H_2O \rightarrow 2LiOH+H_2 \] Magnesium does not react with cold water appreciably. \[ \boxed{\text{Set II is incorrect}} \]

Step 3: Examine Set III \((Na,\ K)\). Both sodium and potassium react vigorously with water. \[ 2Na+2H_2O \rightarrow 2NaOH+H_2 \] \[ 2K+2H_2O \rightarrow 2KOH+H_2 \] \[ \boxed{\text{Set III is correct}} \]

Step 4: Examine Set IV \((K,\ Ca)\). Potassium reacts vigorously with water. Calcium also reacts with cold water. \[ Ca+2H_2O \rightarrow Ca(OH)_2+H_2 \] \[ \boxed{\text{Set IV is correct}} \]

Final Result: The sets in which both metals react with water are \[ \boxed{\text{III and IV only}} \] \[ \boxed{\text{Answer = (C)}} \]