The oxidation state of chlorine in NaClO$_3$ is?

Analyze the question

You are asked for the oxidation state of chlorine (Cl) in sodium chlorate(V), NaClO₃.

Concept

In a neutral compound, the oxidation states of all atoms add up to zero. The rules we use:

• Group 1 metals (like Na) are always +1
• Oxygen is usually -2

Solution

Let the oxidation state of Cl be x.

Na + Cl + 3(O) = 0

(+1) + x + 3(-2) = 0

1 + x - 6 = 0

x - 5 = 0

x = +5

Answer

The oxidation state of chlorine in NaClO₃ is +5, which is option C.

Tip

Memorize the chlorine oxyanion series, since it appears often in exams:

• ClO⁻ (hypochlorite): +1
• ClO₂⁻ (chlorite): +3
• ClO₃⁻ (chlorate): +5
• ClO₄⁻ (perchlorate): +7

The oxidation state goes up by 2 each time you add an oxygen atom. The Roman numeral in a name like "chlorate(V)" also tells you the oxidation state directly.