(A): Oxidation ability increases from `HOCI` to `HCIO_4`
(R): Oxidation number of chlorine increases from `HOCI` to `HCIO_4`. 

Options

A. Both A & R are true, R is the correct explanation of A
B. Both A & R are true, R is not correct explanation of A
C. A is true, R is false
D. A is false, R is true

Answer

To analyze the given assertion and reason, we will follow these steps:

### Step 1: Identify the Compounds
We are dealing with the following compounds:
- HOCl (Hypochlorous acid)
- HClO2 (Chlorous acid)
- HClO3 (Chloric acid)
- HClO4 (Perchloric acid)

### Step 2: Determine the Oxidation States of Chlorine
Next, we will calculate the oxidation states of chlorine in each of these compounds:
1. **HOCl**:
- Hydrogen (H) has an oxidation state of +1.
- Oxygen (O) has an oxidation state of -2.
- Let the oxidation state of Cl be x.
- The equation: +1 + x - 2 = 0 → x = +1.

2. **HClO2**:
- H = +1, O = -2 (2 oxygen atoms contribute -4).
- Let the oxidation state of Cl be y.
- The equation: +1 + y - 4 = 0 → y = +3.

3. **HClO3**:
- H = +1, O = -2 (3 oxygen atoms contribute -6).
- Let the oxidation state of Cl be z.
- The equation: +1 + z - 6 = 0 → z = +5.

4. **HClO4**:
- H = +1, O = -2 (4 oxygen atoms contribute -8).
- Let the oxidation state of Cl be w.
- The equation: +1 + w - 8 = 0 → w = +7.

### Step 3: Analyze the Oxidation States
Now we summarize the oxidation states:
- HOCl: +1
- HClO2: +3
- HClO3: +5
- HClO4: +7

### Step 4: Assess the Assertion and Reason
- **Assertion (A)**: "Oxidation ability increases from HOCl to HClO4."
- **Reason (R)**: "Oxidation number of chlorine increases from HOCl to HClO4."

From our calculations:
- The oxidation ability does not increase from HOCl to HClO4; it actually decreases because HOCl has a lower oxidation state (+1) compared to HClO4 (+7).
- The reason is correct; the oxidation number of chlorine does indeed increase from +1 in HOCl to +7 in HClO4.

### Conclusion
- The assertion is **false**.
- The reason is **true**.

Thus, the correct answer is that the assertion is false and the reason is true.

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