Question

Find the oxidation number of Cl in \(\text{ClO}_4^{-1}\)

• A. \(-9\)
• B. \(+7\)
• C. \(-7\)
• D. \(+9\)

Hint:

Let x be the oxidation number of Cl. Then x + 4(-2) = -1.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
In an ion, the sum of the oxidation numbers of all atoms equals the charge on the ion. Oxygen is \(-2\) in most compounds.

Step 2: Set up the equation:
Let the oxidation number of Cl be \(x\). The ion \(\text{ClO}_4^-\) has a charge of \(-1\).
\[ x + 4(-2) = -1 \]

Step 3: Solve:
\(x - 8 = -1\), so \(x = +7\).

Step 4: Why the other options are wrong.
-9, -7 and +9 are impossible or wrong: chlorine has only 7 valence electrons, so its maximum oxidation state is +7, and -7 would need it to gain 7 electrons.

Final Answer:
The oxidation number of chlorine in perchlorate is +7. \[ \boxed{\text{(B) }+7} \]