Question

What is the number of electrons gained by Cl atom when \(n\) mole of \(\text{ClO}_4^-\) is transformed into \(n\) mole of \(\text{ClO}_2^-\) ion?

• A. \(3n\)
• B. \(4n\)
• C. \(n\)
• D. \(2n\)

Hint:

Find the oxidation number of Cl in each ion and take the difference.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
The number of electrons gained by an atom equals the fall in its oxidation number. We calculate the oxidation number of chlorine in both ions.

Step 2: Chlorine in \(\text{ClO}_4^-\)
\[ x+4(-2)=-1\Rightarrow x=+7 \]

Step 3: Chlorine in \(\text{ClO}_2^-\)
\[ y+2(-2)=-1\Rightarrow y=+3 \]

Step 4: Electrons per Cl atom
\[ +7\to+3\ \text{means}\ 4\ \text{electrons gained per atom} \]

Step 5: For n moles
One mole of Cl atoms gains 4 moles of electrons. So \(n\) mol of \(\text{ClO}_4^-\) gain \(4n\) mol of electrons.

Step 6: Check the options
The other options 3n, n and 2n come from wrong oxidation numbers such as +6 or +5 for the product. The correct answer is option (B).

Final Answer:
Each Cl atom goes from +7 to +3, gaining 4 electrons, so n mol gain 4n electrons, option (B). \[ \boxed{4n} \]