The oxidation number of Cl in Cl₂ is:

• (A) 0
• (B) -1
• (C) +1
• (D) -2
• (E) +2

The oxidation number of chlorine (Cl) in Cl₂ is 0. This is because in its elemental form, each atom of chlorine is in a neutral state, meaning it has not gained or lost any electrons. Let's break this down further to clarify why this is the case.

Understanding Oxidation Numbers

Oxidation numbers, or oxidation states, are a way to keep track of electrons in chemical reactions. They help us understand how atoms interact with each other. The oxidation number can be positive, negative, or zero, depending on the atom's electron configuration and its bonding situation.

Elemental Form and Oxidation States

When an element is in its pure form, such as Cl₂ (which consists of two chlorine atoms bonded together), the oxidation number is always zero. This is true for all diatomic molecules, like O₂ (oxygen) and N₂ (nitrogen), as well as for any element in its uncombined state.

Why Cl₂ Has an Oxidation Number of 0

• Neutral State: Each chlorine atom in Cl₂ shares electrons equally with the other chlorine atom. There is no charge on the molecule, and thus, no change in oxidation state.
• Comparison with Other States: If chlorine were to form compounds, its oxidation number would change. For example, in HCl (hydrochloric acid), chlorine has an oxidation number of -1 because it gains an electron from hydrogen.

Examples of Oxidation Numbers in Compounds

To further illustrate, consider these examples:

• NaCl: In sodium chloride, sodium (Na) has an oxidation number of +1, while chlorine (Cl) has an oxidation number of -1.
• ClO₃: In chlorate (ClO₃⁻), chlorine has an oxidation number of +5, as it is bonded to oxygen, which is more electronegative.

Final Thoughts

In summary, the oxidation number of Cl in Cl₂ is 0 because it is in its elemental state, where there is no net gain or loss of electrons. This concept is fundamental in understanding how elements behave in different chemical environments. So, the correct answer to your question is (A) 0.