The most stable oxidation state of aluminum is `"……………."` while that of thallium is `"………….."`.

Answer

To answer the question regarding the most stable oxidation states of aluminum and thallium, we can follow these steps:

### Step 1: Determine the Electron Configuration of Aluminum
- Aluminum (Al) has an atomic number of 13. Its electron configuration is:
- 1s² 2s² 2p⁶ 3s² 3p¹
- This can also be summarized as having 2 electrons in the first shell, 8 in the second shell, and 3 in the third shell.

### Step 2: Identify the Most Stable Oxidation State of Aluminum
- Aluminum can lose 3 electrons from its outermost shell (3s² 3p¹) to achieve a stable noble gas configuration (similar to neon).
- Therefore, the most stable oxidation state of aluminum is **+3**.

### Step 3: Determine the Electron Configuration of Thallium
- Thallium (Tl) has an atomic number of 81. Its electron configuration is:
- [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹
- This indicates that thallium has 3 electrons in its outermost shell (6s² 6p¹).

### Step 4: Identify the Most Stable Oxidation State of Thallium
- Similar to aluminum, thallium can also lose electrons. However, due to the inert pair effect, the +3 oxidation state becomes less stable as we move down the group.
- The inert pair effect refers to the tendency of the s-electrons (in this case, the 6s² electrons) to remain non-ionized.
- As a result, the most stable oxidation state of thallium is **+1**.

### Final Answer
- The most stable oxidation state of aluminum is **+3** while that of thallium is **+1**.

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