phosphine is generally prepared in the laboratory

Options

A. By heating phosphorus in a current of hydrogen
B. By heating white phosphorus with aqueous solution of caustic potash
C. By decomposition of `P_(2)H_(4) " at " 110^(@)C`
D. By heating red phosphorus with an aqueous solution of caustic soda

Explanation

To prepare phosphine (PH₃) in the laboratory, follow these steps:

### Step-by-Step Solution:

1. **Materials Required**:
- White phosphorus (P₄)
- Aqueous sodium hydroxide (NaOH)
- Water (H₂O)

2. **Set Up the Reaction**:
- In a fume hood or well-ventilated area, take a small amount of white phosphorus and place it in a reaction vessel.
- Add an excess of aqueous sodium hydroxide to the vessel.

3. **Heat the Mixture**:
- Carefully heat the mixture of white phosphorus and aqueous sodium hydroxide. This should be done cautiously as white phosphorus is highly reactive and can ignite spontaneously in air.

4. **Observe the Reaction**:
- As the mixture is heated, phosphine gas (PH₃) will be produced along with sodium hypophosphite (NaH₂PO₂) as a byproduct.

5. **Collect the Phosphine**:
- The phosphine gas can be collected by downward displacement of air or by using a gas jar.

6. **Balanced Chemical Equation**:
- The balanced chemical equation for the reaction is:
\[ P_4 + 4 NaOH + 2 H_2O \rightarrow 2 PH_3 + 2 NaH_2PO_2 \]

### Final Answer:
Phosphine is prepared in the laboratory by heating white phosphorus (P₄) with an excess of aqueous sodium hydroxide (NaOH) and water (H₂O), resulting in phosphine (PH₃) and sodium hypophosphite (NaH₂PO₂).

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