Which of the following is used to reduce `TiCl_4` to Ti?

Options

A. C
B. Al
C. Mg
D. `H_2`

Answer

To solve the question of which substance is used to reduce `TiCl_4` to Ti, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Oxidation States**:
- In `TiCl_4`, titanium (Ti) has an oxidation state of +4. The goal is to reduce it to its elemental form, where the oxidation state is 0.

2. **Understand the Reduction Process**:
- Reduction involves the gain of electrons or a decrease in oxidation state. Here, we need to reduce Ti from +4 to 0.

3. **Identify Reducing Agents**:
- Common reducing agents for titanium chloride include sodium (Na) and magnesium (Mg). Both can effectively reduce `TiCl_4` to titanium.

4. **Write the Reaction with Sodium**:
- When `TiCl_4` reacts with sodium at high temperatures (550°C to 1000°C), the reaction can be represented as:
\[ TiCl_4 + 4Na \rightarrow Ti + 4NaCl \]

5. **Write the Reaction with Magnesium**:
- The Kroll process involves the reduction of `TiCl_4` with magnesium. The reaction can be represented as:
\[ TiCl_4 + 2Mg \rightarrow Ti + 2MgCl_2 \]

6. **Determine the Correct Answer**:
- Both sodium and magnesium can reduce `TiCl_4`, but the Kroll process specifically refers to the use of magnesium. Therefore, the answer to the question is magnesium.

### Final Answer:
The substance used to reduce `TiCl_4` to Ti is **magnesium**.

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