Question

The sum of oxidation states of all atoms in \(\text{Cr}_2\text{O}_7^{2-}\) ion is

• A. Zero
• B. -2
• C. +2
• D. -1

Hint:

To find the sum of oxidation states in a polyatomic ion, balance the charges of the atoms in the ion.

Answer 1

The Correct Option is B

Step 1: Understanding the oxidation states.
In the \(\text{Cr}_2\text{O}_7^{2-}\) ion, the oxidation state of oxygen is -2. For two chromium atoms and seven oxygen atoms, we use the equation: \[ 2 \times \text{Oxidation state of Cr} + 7 \times (-2) = -2 \] Solving this, we get the oxidation state of chromium as +6.
Step 2: Analyzing the options.
(A) Zero: Incorrect, the sum of oxidation states is not zero in this ion.
(B) -2: Correct, the sum of the oxidation states of all atoms in \(\text{Cr}_2\text{O}_7^{2-}\) ion is -2.
(C) +2: Incorrect, this is not the sum of oxidation states in the ion.
(D) -1: Incorrect, this is not the sum of oxidation states in the ion.
Step 3: Conclusion.
The correct answer is (B) -2.