Which reaction is not valid

Options

A. `HCl + F_(2) to HF + Cl_(2)`
B. `HF + Cl_(2) to F_(2) + HCl `
C. `Zn+ HCl to ZnCl_(2) + H_(2)`
D. `Al+ HCl to AlCl_(3) + H_(2)`

Explanation

To determine which reaction is not valid, we will analyze each given reaction step by step.

### Step 1: Analyze the first reaction
**Reaction:** HCl is made from F2 because HF is made from Cl2.

- **Explanation:** The formation of HCl from F2 is valid because F2 can react with HCl to produce HF and Cl2. This means that the reaction is indeed valid.

### Step 2: Analyze the second reaction
**Reaction:** HF + Cl2 → F2.

- **Explanation:** This reaction is presented as a reverse reaction. However, it is not a valid reaction because it does not follow the established chemical behavior of these substances. The reverse of the formation of HF from Cl2 does not yield F2. Therefore, this reaction is not valid.

### Step 3: Analyze the third reaction
**Reaction:** Zn + Cl2 → ZnCl2.

- **Explanation:** This reaction is valid as zinc reacts with chlorine gas to form zinc chloride (ZnCl2). This is a well-known reaction in chemistry.

### Step 4: Analyze the fourth reaction
**Reaction:** Al + HCl → AlCl3 + H2.

- **Explanation:** This reaction is also valid. Aluminum reacts with hydrochloric acid (HCl) to produce aluminum chloride (AlCl3) and hydrogen gas (H2). The stoichiometry of the reaction is also correct.

### Conclusion
After analyzing all the reactions, we conclude that the second reaction (HF + Cl2 → F2) is not valid.

### Final Answer
The reaction that is not valid is: **HF + Cl2 → F2.**

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