The non-metal which does not react with water but reacts with alkali?

Options

A. Boron
B. Bromine
C. `P_4`
D. Fluorine

Explanation

To solve the question of identifying the non-metal that does not react with water but reacts with alkali, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Non-Metals**: The non-metals we are considering are boron (B), bromine (Br), phosphorus (P4), and fluorine (F).

2. **Check Reaction with Water**:
- **Boron (B)**: When boron reacts with water, it forms boron oxide (B2O3) and hydrogen gas (H2). Therefore, boron reacts with water.
- **Bromine (Br)**: When bromine reacts with water, it produces hydrogen bromide (HBr) and oxygen gas (O2). Thus, bromine also reacts with water.
- **Phosphorus (P4)**: Phosphorus does not react with water, indicating it may be a candidate.
- **Fluorine (F)**: Fluorine reacts with water to form hydrofluoric acid (HF) and oxygen gas (O2). Hence, fluorine reacts with water.

3. **Check Reaction with Alkali (Sodium Hydroxide, NaOH)**:
- **Boron (B)**: Boron reacts with sodium hydroxide to form sodium metaborate (NaBO2), sodium oxide (Na2O), and water. Therefore, boron reacts with alkali.
- **Bromine (Br)**: Bromine reacts with sodium hydroxide to form sodium bromide (NaBr) and sodium hypobromite (NaOBr). Hence, bromine also reacts with alkali.
- **Phosphorus (P4)**: Phosphorus reacts with sodium hydroxide to form phosphine gas (PH3) and sodium thiosulfate (NaS2PO2). Therefore, phosphorus reacts with alkali.
- **Fluorine (F)**: Fluorine reacts with sodium hydroxide to form sodium fluoride (NaF) and oxygen difluoride (OF2). Thus, fluorine reacts with alkali.

4. **Conclusion**: Among the non-metals considered, phosphorus (P4) does not react with water but does react with alkali. Therefore, the answer to the question is **P4 (Phosphorus)**.

### Final Answer:
The non-metal which does not react with water but reacts with alkali is **P4 (Phosphorus)**.