In which of the following changes, `Delta H` is always negative :

Options

A. enthalpy of solution
B. enthalpy of hydrogenation
C. enthalpy of reaction
D. enthalpy of transition

Explanation

To determine in which of the following changes ΔH (enthalpy change) is always negative, we need to analyze each option provided.

### Step-by-Step Solution:

1. **Understanding ΔH**:
- ΔH represents the change in enthalpy during a reaction. A negative ΔH indicates that the reaction is exothermic, meaning heat is released.

2. **Option 1: Enthalpy of Solution (ΔHs)**:
- The enthalpy of solution refers to the heat change when a solute dissolves in a solvent. This can be either positive (endothermic, heat absorbed) or negative (exothermic, heat released). Therefore, ΔHs can be both positive or negative, making this option incorrect.

3. **Option 2: Enthalpy of Hydrogenation (ΔHhyd)**:
- Enthalpy of hydrogenation is the heat change when hydrogen is added to an unsaturated compound to form a saturated compound. This process releases heat, indicating that it is exothermic. Therefore, ΔHhyd is always negative. This option is correct.

4. **Option 3: Enthalpy of Reaction (ΔHr)**:
- The enthalpy of reaction is the difference between the total enthalpy of products and reactants. Depending on the nature of the reaction (exothermic or endothermic), ΔHr can be either positive or negative. Thus, this option is incorrect.

5. **Option 4: Enthalpy of Transition (ΔHt)**:
- Enthalpy of transition refers to the heat change during a physical change (e.g., melting, boiling). This can also be either positive (heat absorbed) or negative (heat released). Therefore, this option is also incorrect.

### Conclusion:
The only option where ΔH is always negative is **Option 2: Enthalpy of Hydrogenation**.

### Final Answer:
**Option 2: Enthalpy of Hydrogenation (ΔHhyd)** is always negative.

---