Option 4, Calcium oxide, is the correct answer. When calcium oxide is dissolved in water, heat is evolved. This is because the process of dissolving calcium oxide in water is highly exothermic.
Let`s break down the other options to understand why they are not the correct answers:
- Option 1, Potassium nitrate: When potassium nitrate is dissolved in water, it undergoes an endothermic process, meaning that it absorbs heat rather than releasing it.
- Option 2, Sodium chloride: When sodium chloride, or table salt, is dissolved in water, it also undergoes an endothermic process.
- Option 3, Glucose: Dissolving glucose in water does not produce heat. This process is neither exothermic nor endothermic, meaning that it does not release or absorb heat.
In summary, only calcium oxide, option 4, releases heat when dissolved in water, making it the correct answer.