Assertion: Alkaline earth metal oxides are quite stable to heat.
Reason: Enthalpies of formation of alkaline earth metal oxides are quite high.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Answer

To determine the validity of the assertion and reason provided in the question, we will analyze both statements step by step.

### Step 1: Understanding the Assertion
**Assertion:** Alkaline earth metal oxides are quite stable to heat.

- Alkaline earth metals include elements like Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), and Barium (Ba).
- When these metals react with oxygen, they form their respective oxides (e.g., BeO, MgO, CaO, SrO, BaO).
- These metal oxides are known to be stable when subjected to heat, meaning they do not decompose easily upon heating.

### Step 2: Understanding the Reason
**Reason:** Enthalpies of formation of alkaline earth metal oxides are quite high.

- The enthalpy of formation refers to the change in energy when one mole of a compound is formed from its elements in their standard states.
- For alkaline earth metal oxides, the enthalpy of formation is indeed high, indicating that a significant amount of energy is released when these oxides are formed.
- This high enthalpy of formation contributes to the stability of the oxides because it implies that the products (metal oxides) are lower in energy compared to the reactants (metal and oxygen), making them less likely to decompose back into their constituent elements.

### Step 3: Conclusion
- Since the assertion states that alkaline earth metal oxides are stable to heat and the reason explains that this stability is due to their high enthalpy of formation, both statements are true.
- Moreover, the reason correctly explains why the assertion is valid.

### Final Answer:
Both the assertion and the reason are true, and the reason correctly explains the assertion.