Assertion: `HClO_(4)` is a stronger acid than `HClO_(3)`.
Reason: Oxidation state of `Cl` in `HClO_(4)` is `+VII` and in `HClO_(3)+V`.

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 solve the question regarding the assertion and reason about the acids HClO4 and HClO3, we can follow these steps:

### Step 1: Understand the assertion
The assertion states that HClO4 (perchloric acid) is a stronger acid than HClO3 (chloric acid).

### Step 2: Analyze the structure of HClO4 and HClO3
- **HClO4 Structure**: HClO4 has one chlorine atom bonded to four oxygen atoms, with one of the oxygen atoms connected to a hydrogen atom (the hydroxyl group). The chlorine has a +7 oxidation state.
- **HClO3 Structure**: HClO3 has one chlorine atom bonded to three oxygen atoms, with one of the oxygen atoms connected to a hydrogen atom. The chlorine has a +5 oxidation state.

### Step 3: Determine the acidity
The strength of an acid is influenced by the ability to donate protons (H+ ions). The more electronegative atoms surrounding the central atom (chlorine, in this case), the more they can stabilize the negative charge that results when the acid donates a proton.

- In HClO4, the presence of four oxygen atoms allows for greater stabilization of the negative charge after the proton is released, making it a stronger acid.
- In HClO3, with only three oxygen atoms, there is less stabilization of the negative charge, making it a weaker acid compared to HClO4.

### Step 4: Evaluate the reason
The reason given is that the oxidation state of chlorine in HClO4 is +7, while in HClO3 it is +5. This statement is correct, but the oxidation state itself does not directly determine the acidity. Instead, it is the number of oxygen atoms that plays a more significant role in determining the strength of the acid.

### Step 5: Conclusion
- Both the assertion and the reason are true.
- However, the reason provided does not correctly explain why HClO4 is a stronger acid than HClO3. The strength of the acid is more closely related to the number of oxygen atoms rather than the oxidation state of chlorine.

### Final Answer
Both assertion and reason are true, but the reason is not the correct explanation of the assertion. Therefore, the correct option is:
**B: Both assertion and reason are true, but reason is not the correct explanation of assertion.**