Beryllium shows diagonal relationship with aluminium. Which of the following similarly is incorrect?

Options

A. `Be_(2)C` like `Al_(4)C_(3)` yields methane on hydrolysis
B. Be like Al is rendered passive by `HNO_(3)`
C. `Be(OH)_(2)` like `Al(OH)_(3)` is basic
D. Be forms beryllates and Al forms aluminates.

Explanation

To solve the question regarding the diagonal relationship between beryllium and aluminum, and to identify which similarity is incorrect among the given options, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Diagonal Relationship**:
- Beryllium (Be) and Aluminum (Al) exhibit a diagonal relationship in the periodic table. This means they share some similar properties due to their similar charge-to-radius ratios, despite being in different groups.

2. **Analyzing the Options**:
- We need to analyze each option provided to determine which one is incorrect.

3. **Option A**: "Beryllium carbide and aluminum carbide yield methane on hydrolysis."
- **Analysis**:
- Beryllium carbide (Be2C) reacts with water to produce beryllium hydroxide and methane.
- Aluminum carbide (Al4C3) also reacts with water to produce aluminum hydroxide and methane.
- Both yield methane upon hydrolysis, so this statement is **true**.

4. **Option B**: "Beryllium and aluminum form passive layers by HNO3."
- **Analysis**:
- Both beryllium and aluminum react with nitric acid (HNO3) to form a passive oxide layer, making them resistant to further corrosion.
- This statement is also **true**.

5. **Option C**: "Beryllium hydroxide and aluminum hydroxide are basic."
- **Analysis**:
- Beryllium hydroxide (Be(OH)2) is amphoteric, meaning it can react with both acids and bases. It behaves more like an acid in some reactions.
- Aluminum hydroxide (Al(OH)3) is also amphoteric.
- Therefore, stating that both are basic is **incorrect**.

6. **Option D**: "Beryllium forms berylate and aluminum forms aluminate."
- **Analysis**:
- Beryllium forms berylate (NaBeO2) and aluminum forms aluminate (NaAlO2).
- This statement is **true**.

7. **Conclusion**:
- Since option C is the only statement that is incorrect, the answer to the question is **C**.

### Final Answer:
The incorrect similarity is **C**: "Beryllium hydroxide and aluminum hydroxide are basic."