Assertion. Gay Lussac's law does not follow from Dalton's atomic theory.
Reason. Dalton's atomic theory explains law of chemical combination by mass only.

Options

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

Explanation

To analyze the assertion and reason provided in the question, we will break down the concepts involved step by step.

### Step 1: Understand Gay Lussac's Law
Gay Lussac's law states that when gases react together at constant temperature and pressure, the volumes of the reacting gases and the volumes of the products (if gaseous) are in simple whole number ratios. For example, in the reaction of hydrogen and chlorine to form hydrogen chloride gas, the volumes of hydrogen and chlorine that react are in the ratio of 1:1, and the volume of hydrogen chloride produced is in the ratio of 2.

**Hint:** Remember that Gay Lussac's law deals with the volumes of gases and their ratios during reactions.

### Step 2: Understand Dalton's Atomic Theory
Dalton's atomic theory explains that matter is made up of atoms, which are indivisible particles. It primarily focuses on the concept of mass and the law of conservation of mass. Dalton's theory states that in a chemical reaction, atoms are rearranged, but the total mass remains constant.

**Hint:** Dalton's atomic theory emphasizes mass and the behavior of atoms, not the volumes of gases.

### Step 3: Analyze the Assertion
The assertion states that Gay Lussac's law does not follow from Dalton's atomic theory. This is correct because Dalton's atomic theory does not address the behavior of gases in terms of volume ratios. Instead, it focuses on mass and the conservation of mass during chemical reactions.

**Hint:** Consider how Dalton's theory relates to mass rather than the volume ratios of gases.

### Step 4: Analyze the Reason
The reason states that Dalton's atomic theory explains the law of chemical combination by mass only. This is also correct, as Dalton's theory does not incorporate the concept of gas volumes or their ratios in reactions.

**Hint:** Think about how Dalton's theory limits its explanation to mass and does not extend to gas behavior.

### Step 5: Conclusion
Both the assertion and the reason are correct. The assertion correctly states that Gay Lussac's law does not follow from Dalton's atomic theory, and the reason accurately explains that Dalton's theory focuses solely on mass.

**Final Answer:** Both the assertion and reason are true, and the reason correctly explains the assertion. Therefore, the answer is that the assertion is true, and the reason is a correct explanation of the assertion.