Be and Al exhibit diagonal relationship . Which of the following statements about them is/are not true ?
(i) Both react with HCl to liberate `H_2`.
(ii) They are made passive by `HNO_3`.
(iii) Their carbides give acetylene on treatment with water .
(iv) Their oxides are amphoteric .

Options

A. (iii) and (iv)
B. (i) and (iii)
C. (i) only
D. (iii) only

Explanation

To determine which statements about Beryllium (Be) and Aluminum (Al) are not true, we will analyze each statement one by one.

### Step 1: Analyze Statement (i)
**Statement:** Both react with HCl to liberate H₂.

- **Beryllium Reaction with HCl:**
\[ \text{Be} + 2\text{HCl} \rightarrow \text{BeCl}_2 + \text{H}_2 \]
- **Aluminum Reaction with HCl:**
\[ 2\text{Al} + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2 \]

**Conclusion:** Both metals react with HCl to liberate hydrogen gas (H₂). Therefore, this statement is **true**.

### Step 2: Analyze Statement (ii)
**Statement:** They are made passive by HNO₃.

- **Beryllium Reaction with HNO₃:**
- Beryllium reacts with HNO₃ to form beryllium oxide (BeO), creating a passive layer.

- **Aluminum Reaction with HNO₃:**
- Aluminum also forms aluminum oxide (Al₂O₃) when reacting with HNO₃, which prevents further reaction.

**Conclusion:** Both metals become passive due to the formation of an oxide layer. Therefore, this statement is **true**.

### Step 3: Analyze Statement (iii)
**Statement:** Their carbides give acetylene on treatment with water.

- **Beryllium Carbide (Be₂C):**
- When Be₂C reacts with water, it produces methane (CH₄), not acetylene (C₂H₂).

- **Aluminum Carbide (Al₄C₃):**
- When Al₄C₃ reacts with water, it also produces methane (CH₄), not acetylene.

**Conclusion:** This statement is **not true** because neither carbide produces acetylene on treatment with water.

### Step 4: Analyze Statement (iv)
**Statement:** Their oxides are amphoteric.

- **Beryllium Oxide (BeO):**
- BeO is amphoteric; it reacts with both acids and bases.

- **Aluminum Oxide (Al₂O₃):**
- Al₂O₃ is also amphoteric; it reacts with acids and bases.

**Conclusion:** Both oxides are amphoteric. Therefore, this statement is **true**.

### Final Conclusion
The only statement that is **not true** is statement (iii).

### Answer:
The statement that is not true is (iii): Their carbides give acetylene on treatment with water.

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