OXIDATION NUMBER

Free elements are assigned an oxidation number of 0.

Which one of the following statements is incorrect?

• The oxidation number of sodium (Na) in the metal sodium is 0.

• Ions cannot have an oxidation number of 0.

• The oxidation number of calcium in the calcium ion (Ca²⁺) is 0.

• The oxidation number of hydrogen in the hydrogen molecule (H₂) is 0.

What is the oxidation number of chlorine in KClO₃?

• -1

• +5

• +3

• +1

The alkaline earth metals (Be, Mg, Ca, Sr, Ba, and Ra) are always assigned an oxidation state of +2.

What is the oxidation number of sulfur in magnesium sulfide (MgS)?

• -1

• -2

• +1

• +2

What are the oxidation numbers of copper on the left and right hand sides of the following equation?

Cu + 2AgNO₃ → 2Ag + Cu(NO₃)₂

• +1 and +2

• 0 and +2

• -1 and -2

• 0 and -2

Oxygen in a compound has an oxidation number of -2. One of the exceptions to this rule is when oxygen

• is bonded to hydrogen in water.

• is bonded to chlorine.

• is bonded to a metal forming a metallic oxide.

• is bonded to the more electronegative fluorine.

When mercuric oxide is heated it breaks down to mercury and oxygen as follows:

HgO → Hg + O₂

What is the oxidation number of mercury in mercuric oxide?

• +1

• +2

• -1

• -2

What are the oxidation numbers of the elements in sulfuric acid, H₂SO₄?

• H = +2, S = +6, O = -8

• H = +2, S = +1, O = +4

• H = +1, S = +4, O = -2

• H = +1, S = +6, O = -2

The oxidation number of a monatomic ion equals the charge on the ion.

Which one of the following statements is correct?

• The oxidation number of the hydroxide ion (OH^-) is -1.

• Every atom may have only one oxidation number.

• The oxidation of the fluoride ion is 0.

• The oxidation number of aluminium in the Al³⁺ ion is +3.

Which one of the following elements can only have one oxidation number?

• Chromium

• Fluorine

• Oxygen

• Hydrogen

Which one of the following elements does NOT have a fixed oxidation number?

• Sodium

• Sulfur

• Fluorine

• Magnesium