Which reaction involves neither oxidation nor reduction?

Options

A. `CrO_(4)^(2-) rarr Cr_(2)O_(7)^(2-)`
B. `Cr rarr CrCl_(3)`
C. `KMnO_(4) rarr MnO_(2)`
D. `Fe rarr Fe_(2)O_(3)*xH_(2)O`

Answer

To determine which reaction involves neither oxidation nor reduction, we need to analyze the oxidation states of the elements involved in the reactions. Oxidation is defined as the loss of electrons or an increase in oxidation state, while reduction is defined as the gain of electrons or a decrease in oxidation state.

Let's break down the steps to find the correct answer:

### Step 1: Understand Oxidation and Reduction
- **Oxidation**: Loss of electrons or increase in oxidation number.
- **Reduction**: Gain of electrons or decrease in oxidation number.

### Step 2: Analyze the Given Reactions
We will examine the oxidation states of the elements in each reaction to identify any changes.

#### Reaction A: CrO4 (Chromate)
1. Assume the oxidation state of chromium (Cr) is \( x \).
2. Oxygen has an oxidation state of -2. Therefore, in \( \text{CrO}_4 \):
\[ x + 4(-2) = -2 \quad \Rightarrow \quad x - 8 = -2 \quad \Rightarrow \quad x = +6 \]

#### Reaction B: Cr2O7 (Dichromate)
1. Assume the oxidation state of chromium (Cr) is \( 2x \).
2. In \( \text{Cr}_2\text{O}_7 \):
\[ 2x + 7(-2) = -2 \quad \Rightarrow \quad 2x - 14 = -2 \quad \Rightarrow \quad 2x = 12 \quad \Rightarrow \quad x = +6 \]

#### Reaction C: MnO4 (Permanganate)
1. Assume the oxidation state of manganese (Mn) is \( x \).
2. In \( \text{MnO}_4 \):
\[ x + 4(-2) = -1 \quad \Rightarrow \quad x - 8 = -1 \quad \Rightarrow \quad x = +7 \]

#### Reaction D: Fe2O3 (Iron(III) oxide)
1. Assume the oxidation state of iron (Fe) is \( 2x \).
2. In \( \text{Fe}_2\text{O}_3 \):
\[ 2x + 3(-2) = 0 \quad \Rightarrow \quad 2x - 6 = 0 \quad \Rightarrow \quad 2x = 6 \quad \Rightarrow \quad x = +3 \]

### Step 3: Identify Changes in Oxidation States
- In reactions A, B, C, and D, there are changes in oxidation states:
- Cr in CrO4 and Cr2O7 shows oxidation state changes.
- Mn in MnO4 shows oxidation state changes.
- Fe in Fe2O3 shows oxidation state changes.

### Step 4: Determine the Reaction with No Change
To find a reaction that involves neither oxidation nor reduction, we need to look for a reaction where the oxidation states of all elements remain unchanged.

### Conclusion
After analyzing the oxidation states, we find that the reaction involving **water and hydration does not change oxidation states**, indicating that it involves neither oxidation nor reduction.

### Final Answer
The reaction that involves neither oxidation nor reduction is the one where the oxidation states of all elements remain unchanged.

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