Oxidation number of Cr in ` K_ 2 Cr _ 2 O _ 7, CrO _ 5 and Cr _ 2 (SO _ 4 ) _ 3 ` respectively, is -

Options

A. ` + 6, + 10, + 3 `
B. ` + 6, + 4, + 6 `
C. ` + 6, + 6, + 3 `
D. ` + 6, + 3 , + 3 `

Explanation

To determine the oxidation number of chromium (Cr) in the compounds \( K_2Cr_2O_7 \), \( CrO_5 \), and \( Cr_2(SO_4)_3 \), we will follow a systematic approach for each compound.

### Step 1: Calculate the oxidation number of Cr in \( K_2Cr_2O_7 \)

1. **Identify the known oxidation states**:
- Potassium (K) has an oxidation state of \( +1 \).
- Oxygen (O) has an oxidation state of \( -2 \).

2. **Set up the equation**:
- The formula for potassium dichromate is \( K_2Cr_2O_7 \).
- The total charge must equal zero for a neutral compound.
- The equation can be set up as:
\[ 2(+1) + 2x + 7(-2) = 0 \]
where \( x \) is the oxidation state of chromium.

3. **Solve the equation**:
\[ 2 + 2x - 14 = 0 \\ 2x - 12 = 0 \\ 2x = 12 \\ x = 6 \]

4. **Conclusion**:
- The oxidation number of Cr in \( K_2Cr_2O_7 \) is \( +6 \).

### Step 2: Calculate the oxidation number of Cr in \( CrO_5 \)

1. **Identify the known oxidation states**:
- Oxygen in peroxides has an oxidation state of \( -1 \) (4 O in peroxide) and one O has an oxidation state of \( -2 \).

2. **Set up the equation**:
- The formula for chromium pentoxide is \( CrO_5 \).
- The equation can be set up as:
\[ x + 4(-1) + (-2) = 0 \]

3. **Solve the equation**:
\[ x - 4 - 2 = 0 \\ x - 6 = 0 \\ x = 6 \]

4. **Conclusion**:
- The oxidation number of Cr in \( CrO_5 \) is \( +6 \).

### Step 3: Calculate the oxidation number of Cr in \( Cr_2(SO_4)_3 \)

1. **Identify the known oxidation states**:
- The sulfate ion \( SO_4^{2-} \) has an oxidation state of \( -2 \).

2. **Set up the equation**:
- The formula for chromium sulfate is \( Cr_2(SO_4)_3 \).
- The equation can be set up as:
\[ 2x + 3(-2) = 0 \]

3. **Solve the equation**:
\[ 2x - 6 = 0 \\ 2x = 6 \\ x = 3 \]

4. **Conclusion**:
- The oxidation number of Cr in \( Cr_2(SO_4)_3 \) is \( +3 \).

### Final Results

- The oxidation numbers of Cr in the compounds are:
- \( K_2Cr_2O_7 \): \( +6 \)
- \( CrO_5 \): \( +6 \)
- \( Cr_2(SO_4)_3 \): \( +3 \)

### Summary of Answers
- The oxidation numbers of Cr in \( K_2Cr_2O_7 \), \( CrO_5 \), and \( Cr_2(SO_4)_3 \) are \( +6, +6, +3 \) respectively.