The answer to each of the following questions is a non- negative integer.
`TII_(3)` is isomorphic with `CsI_3` and then the oxidation state of Tl in `TII_3` is………

Answer

To determine the oxidation state of Thallium (Tl) in the compound \( \text{TlI}_3 \), we can follow these steps:

### Step 1: Understand the Isomorphic Relationship
We are given that \( \text{TlI}_3 \) is isomorphic with \( \text{CsI}_3 \). This means that the structure and stoichiometry of both compounds are similar.

### Step 2: Analyze the Composition of \( \text{CsI}_3 \)
In \( \text{CsI}_3 \):
- Cesium (Cs) has an oxidation state of +1.
- Iodine (I) typically has an oxidation state of -1.

The formula can be broken down as:
\[ \text{Cs}^{+1} + 3 \text{I}^{-1} \]

### Step 3: Calculate the Total Charge in \( \text{CsI}_3 \)
The total charge from the iodide ions in \( \text{CsI}_3 \) is:
\[ 3 \times (-1) = -3 \]
To balance this, the charge from cesium is +1, leading to a net charge of:
\[ +1 + (-3) = -2 \]

### Step 4: Analyze the Composition of \( \text{TlI}_3 \)
Since \( \text{TlI}_3 \) is isomorphic to \( \text{CsI}_3 \), it will have a similar structure:
- Let the oxidation state of Thallium (Tl) be \( x \).
- The total charge from the three iodide ions remains the same:
\[ 3 \text{I}^{-1} = -3 \]

### Step 5: Set Up the Equation for \( \text{TlI}_3 \)
The equation for the total charge in \( \text{TlI}_3 \) can be set up as follows:
\[ x + 3(-1) = 0 \]
This simplifies to:
\[ x - 3 = 0 \]

### Step 6: Solve for the Oxidation State of Thallium
Solving the equation gives:
\[ x = 3 \]

### Conclusion
Thus, the oxidation state of Thallium (Tl) in \( \text{TlI}_3 \) is +1.

### Final Answer
The oxidation state of Tl in \( \text{TlI}_3 \) is **1**.

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