Thallium exhibits `+1` and `+3` oxidation states.
Thallium exhibits inert pair effect.

Answer

To solve the question regarding thallium's oxidation states and the inert pair effect, we can break it down into clear steps:

### Step 1: Understanding Oxidation States
Thallium (Tl) can exhibit two oxidation states: +1 and +3. The +1 oxidation state occurs when thallium loses one electron, while the +3 oxidation state occurs when it loses three electrons.

### Step 2: Electronic Configuration of Thallium
The electronic configuration of thallium is:
\[ \text{Tl: [Xe]} \, 4f^{14} \, 5d^{10} \, 6s^2 \, 6p^1 \]

### Step 3: Explanation of the Inert Pair Effect
The inert pair effect refers to the tendency of the two electrons in the outermost s orbital (in this case, the 6s electrons) to remain non-bonding or "inert." This occurs due to the poor shielding effect of the d and f electrons, which makes it energetically unfavorable for these s electrons to participate in bonding.

### Step 4: Relation Between Inert Pair Effect and Oxidation States
Due to the inert pair effect, thallium tends to lose only one of the 6p electrons to achieve the +1 oxidation state, while the 6s electrons remain. If both the 6p and one of the 6s electrons are removed, thallium achieves the +3 oxidation state.

### Step 5: Conclusion
Thus, thallium exhibits both +1 and +3 oxidation states due to the inert pair effect, which explains the reluctance of the s electrons to participate in bonding.

### Final Answer:
Thallium exhibits +1 and +3 oxidation states due to the inert pair effect, which is the reluctance of the s electrons to participate in bonding.

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