Assertion `:` Neopentene forms only one monosubstituted compound.
Reason `:` Neopentane has high bond energy

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Understand the Assertion
The assertion states that neopentene forms only one monosubstituted compound.

- **Neopentene Structure**: Neopentene is a branched alkene with the formula C5H10. Its structure can be represented as follows:

```
CH3
|
CH3-C-CH3
|
CH2
```

- **Monosubstitution**: When we talk about monosubstitution, we mean replacing one hydrogen atom with another atom or group (like a chlorine atom).

- **Equivalent Carbons**: In neopentene, the four outer carbon atoms (methyl groups) are equivalent. This means that replacing any one of the hydrogen atoms on these carbons will yield the same product.

### Conclusion for Step 1:
Thus, the assertion is correct: neopentene does indeed form only one monosubstituted compound due to the equivalence of the outer carbon atoms.

### Step 2: Understand the Reason
The reason states that neopentane has high bond energy.

- **Bond Energy**: Bond energy refers to the amount of energy required to break a bond between two atoms. While it is true that neopentane (the saturated counterpart of neopentene) has strong C-H bonds, the assertion about monosubstitution does not depend on bond energy.

- **Relevance to Assertion**: The reason provided does not explain why neopentene has only one monosubstituted compound. The equivalence of the hydrogen atoms is the key factor, not the bond energy.

### Conclusion for Step 2:
The reason is incorrect in this context. The assertion is true, but the reason is false.

### Final Answer:
- Assertion: True
- Reason: False