(A): `TlCl_3` acts as a good oxidant
(R): `Tl^(+3)` is less stable than `Tl^+`

Options

A. A and R are true, R explains A
B. A and R are true, R does not explain A
C. A is true, but R is false
D. A is false, but R is true

Answer

To solve the question regarding the assertion (A) and reason (R), we will analyze both statements step by step.

### Step 1: Analyze the Assertion (A)
The assertion states that **TlCl₃ acts as a good oxidant**.

- **Explanation**: An oxidizing agent (or oxidant) is a substance that can accept electrons and, in the process, is reduced while causing the oxidation of another substance. In this case, TlCl₃ can indeed act as a good oxidizing agent because it can oxidize other substances while itself being reduced.

### Step 2: Analyze the Reason (R)
The reason states that **Tl^(+3) is less stable than Tl^(+1)**.

- **Explanation**: The stability of oxidation states can vary among elements. For thallium (Tl), the +3 oxidation state (Tl^(+3)) is indeed less stable compared to the +1 oxidation state (Tl^(+1)). This is because Tl^(+1) is more stable due to the inert pair effect, where the s-electrons are less likely to participate in bonding, making the +1 state more favorable.

### Step 3: Establish the Relationship Between A and R
Now we need to determine if the reason (R) explains the assertion (A).

- **Explanation**: Since TlCl₃ can oxidize other substances while being reduced itself, and since Tl^(+3) is less stable than Tl^(+1), the reason (R) does explain why TlCl₃ acts as a good oxidant. The instability of Tl^(+3) makes it more likely to gain an electron and be reduced to Tl^(+1), thus facilitating its role as an oxidizing agent.

### Conclusion
Both the assertion (A) and the reason (R) are true, and the reason explains the assertion. Therefore, the correct answer is that both A and R are true, and R explains A.

### Final Answer
**A and R are true; R explains A.**

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