Question

Identify the reaction in which hydrogen gas is not liberated

• A. \( Al(s) + HCl(aq) \rightarrow \)
• B. \( NaBH_4 + I_2 \rightarrow \)
• C. \( BF_3 + LiAlH_4 \rightarrow \)
• D. \( Al(s) + NaOH(aq) \rightarrow \)

Hint:

- Aluminium reacts with both HCl and NaOH to liberate \( H_2 \) gas.
- \( NaBH_4 \) reacts with iodine to release hydrogen gas.
- \( BF_3 \) reacts with \( LiAlH_4 \) but does NOT liberate hydrogen gas.

Answer 1

The Correct Option is C

Step 1: Understanding the Liberation of Hydrogen Gas in the Given Reactions 
- Reaction 1: \( Al + HCl \) 
- Aluminium reacts with hydrochloric acid to form aluminium chloride and liberates hydrogen gas: \[ 2Al + 6HCl \rightarrow 2AlCl_3 + 3H_2 \] 
- Hydrogen gas is liberated. 
- Reaction 2: \( NaBH_4 + I_2 \) 
- Sodium borohydride reacts with iodine to form hydrogen gas: \[ NaBH_4 + 2I_2 \rightarrow BI_3 + NaI + 2H_2 \] 
- Hydrogen gas is liberated. 
- Reaction 3: \( BF_3 + LiAlH_4 \) 
- Lithium aluminium hydride (\( LiAlH_4 \)) is used as a reducing agent. 
- No hydrogen gas is released in this reaction. 
- Reaction 4: \( Al + NaOH \) 
- Aluminium reacts with sodium hydroxide in water to form sodium aluminate and liberates hydrogen gas: \[ 2Al + 2NaOH + 6H_2O \rightarrow 2Na[Al(OH)_4] + 3H_2 \] 
- Hydrogen gas is liberated. 

Step 2: Identifying the Correct Answer 
- The only reaction where hydrogen gas is NOT liberated is \( BF_3 + LiAlH_4 \). 
- Option (3) is correct.