`MnO_(2)` is the most important oxide of manganese , `MnO_(2)` occurs natually as the black coloured mineral pyrolusite. It is an oxidising agent, and decomposes to `Mn_(3)O_(4)` on heating to `530^(@)`C. It is used in the preparation of potassium permanaganate and in the productioon of `Cl_(2)` gas. Over half million tonnes per year of `MnO_(2)` is used in dry batteries.
Q. `MnO_(2)` dissolves in concentrated HCl to form:

Options

A. `Mn^(4+)` ion and `Cl_(2)`
B. `Mn^(2+)` ion and `Cl_(2)`
C. `[MnCl_(4)]^(2-) and Cl_(2)`
D. only `[MnCl_(4)]^(2-)`

Answer

To solve the question of what `MnO2` forms when it dissolves in concentrated HCl, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactants in this reaction are manganese dioxide (`MnO2`) and concentrated hydrochloric acid (`HCl`).

2. **Understand the Reaction**: When `MnO2` is treated with concentrated HCl, it acts as an oxidizing agent. This means it can oxidize other substances while being reduced itself.

3. **Write the Reaction**: The balanced chemical reaction for the dissolution of `MnO2` in concentrated HCl can be represented as:
\[ MnO_2 + 4HCl \rightarrow MnCl_2 + 2Cl_2 + 2H_2O \]
Here, `MnO2` reacts with `HCl` to produce manganese chloride (`MnCl2`), chlorine gas (`Cl2`), and water (`H2O`).

4. **Analyze the Products**: From the balanced equation, we can see that the products formed are:
- Manganese(II) chloride (`MnCl2`)
- Chlorine gas (`Cl2`)

5. **Determine the Oxidation States**:
- In `MnO2`, manganese is in the +4 oxidation state.
- In `MnCl2`, manganese is in the +2 oxidation state.
- Chlorine in HCl is in the -1 oxidation state and is oxidized to 0 in `Cl2`.

6. **Conclusion**: The products of the reaction are manganese ions (`Mn^2+`) and chlorine gas (`Cl2`). Therefore, when `MnO2` dissolves in concentrated HCl, it forms `MnCl2` and `Cl2`.

### Final Answer:
When `MnO2` dissolves in concentrated HCl, it forms `MnCl2` and `Cl2`.

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