Oxidation number of Cr atom in `CrO_(5) " and "K_(3)CrO_(8)` respectively

Options

A. `+6, +6`
B. `+5, +6`
C. `+6, +5`
D. `+5, +5`

Answer

To find the oxidation number of chromium (Cr) in the compounds CrO5 and K3CrO8, we will follow a systematic approach.

### Step 1: Determine the oxidation number of Cr in CrO5

1. **Assign oxidation states**:
- Let the oxidation number of Cr be \( x \).
- The oxidation number of oxygen (O) is typically \(-2\).

2. **Set up the equation**:
- In CrO5, there are 5 oxygen atoms. Therefore, the total contribution from oxygen is \( 5 \times (-2) = -10 \).
- The overall charge of the compound is neutral (0), so we can set up the equation:
\[ x + 5(-2) = 0 \]
- This simplifies to:
\[ x - 10 = 0 \]
- Solving for \( x \):
\[ x = +10 \]

3. **Check for validity**:
- The maximum oxidation state of chromium is +6 (as it can lose up to 6 electrons). Therefore, an oxidation state of +10 is not possible. This indicates that CrO5 contains a peroxo linkage.

4. **Re-evaluate with peroxo linkage**:
- In peroxides, the oxidation state of O is \(-1\). In CrO5, there are 4 oxygen atoms in the form of peroxides and 1 in the typical \(-2\) state.
- Thus, we can revise our equation:
\[ x + 4(-1) + (-2) = 0 \]
- This simplifies to:
\[ x - 4 - 2 = 0 \implies x - 6 = 0 \implies x = +6 \]

### Step 2: Determine the oxidation number of Cr in K3CrO8

1. **Assign oxidation states**:
- Let the oxidation number of Cr be \( x \).
- The oxidation number of potassium (K) is \( +1 \) and oxygen is typically \(-2\).

2. **Set up the equation**:
- There are 3 potassium atoms contributing \( 3 \times (+1) = +3 \).
- There are 8 oxygen atoms contributing \( 8 \times (-2) = -16 \).
- The overall charge of the compound is neutral (0), so we can set up the equation:
\[ 3 + x + 8(-2) = 0 \]
- This simplifies to:
\[ 3 + x - 16 = 0 \implies x - 13 = 0 \implies x = +13 \]

3. **Check for validity**:
- The oxidation state cannot be +13 for chromium. This indicates that there are some oxygen atoms in a different oxidation state.
- In K3CrO8, we can assume that 2 of the oxygen atoms are in the form of peroxides (with an oxidation state of -1).
- Therefore, we can revise our equation:
\[ 3 + x + 6(-2) + 2(-1) = 0 \]
- This simplifies to:
\[ 3 + x - 12 - 2 = 0 \implies x - 11 = 0 \implies x = +5 \]

### Final Answers:
- The oxidation number of Cr in CrO5 is **+6**.
- The oxidation number of Cr in K3CrO8 is **+5**.