Question

The oxidation number of chromium in potassium dichromate is

• A. 6
• B. 4
• C. 3
• D. 2

Answer 1

The Correct Option is A

 To determine the oxidation number of chromium in potassium dichromate (\(\text{K}_2\text{Cr}_2\text{O}_7\)), we follow a systematic approach to assign oxidation states to each element while ensuring the compound's overall charge is zero.

1. Start by assigning oxidation numbers to the known elements. Potassium (\(\text{K}\)) typically has an oxidation number of +1. For \(\text{K}_2\text{Cr}_2\text{O}_7\), there are two potassium ions, contributing a total oxidation number of \(2 \times (+1) = +2\).
2. Oxygen (\(\text{O}\)) usually has an oxidation number of -2. In \(\text{K}_2\text{Cr}_2\text{O}_7\), there are seven oxygen atoms, contributing a total oxidation number of \(7 \times (-2) = -14\).
3. Assign the oxidation number of chromium (\(\text{Cr}\)) as \(x\). Since there are two chromium atoms present, the contribution is \(2x\).
4. For the compound \(\text{K}_2\text{Cr}_2\text{O}_7\) to be electrically neutral, the sum of oxidation numbers of all atoms must be zero. Therefore:

2(+1) + 2x + 7(-2) = 0

Solving the equation:

• \(2 + 2x - 14 = 0\)
• \(2x - 12 = 0\)
• \(2x = 12\)
• \(x = 6\)

Thus, the oxidation number of chromium in potassium dichromate is +6. This matches with the correct answer option provided:

6

.