Oxidation Number Practice Worksheet

Give the oxidation number of the indicated atoms/ion.

N in N₂O₃

• +3

• +2

• +5

• 0

Answer explanation

In N₂O₃, the oxidation state of oxygen is -2. With three oxygens, the total is -6. To balance this, the two nitrogen atoms must have a total oxidation state of +6, giving each nitrogen an oxidation number of +3.

Give the oxidation number of the indicated atoms/ion.

S in H₂SO₄

• +6

• +3

• 0

• +4

Answer explanation

In H₂SO₄, the oxidation state of sulfur (S) can be calculated. Each hydrogen (H) is +1, and each oxygen (O) is -2. The total charge of the molecule is 0. Thus, S must be +6 to balance the charges, making the correct answer +6.

Give the oxidation number of the indicated atoms/ion.

C in C

• 0

• +2

• -4

• +4

Answer explanation

The oxidation number of an element in its elemental form is always 0. Since carbon (C) in C is in its elemental state, its oxidation number is 0, making the correct choice 0.

Give the oxidation number of the indicated atoms/ion.

C in CO

• +2

• -2

• 0

• +1

Answer explanation

In CO, carbon (C) has an oxidation number of +2. This is because oxygen (O) typically has an oxidation number of -2, and to balance the overall charge of the molecule (which is neutral), carbon must be +2.

Give the oxidation number of the indicated atoms/ion.

Na in NaCl

• +2

• +1

• 0

• -1

Answer explanation

In NaCl, sodium (Na) has an oxidation number of +1. This is because Na loses one electron to achieve a stable electron configuration, resulting in a positive charge.

Give the oxidation number of the indicated atoms/ion.

H in H₂O

• -1

• +2

• +1

• 0

Answer explanation

In H₂O, hydrogen (H) has an oxidation number of +1. Each hydrogen atom contributes +1, while oxygen (O) is -2, balancing the overall charge of the molecule to zero.

Give the oxidation number of the indicated atoms/ion.

Ba in BaCl₂

• +2

• +1

• 0

• -2

Answer explanation

In BaCl₂, barium (Ba) is a Group 2 element, which typically has an oxidation number of +2. Chlorine (Cl) has an oxidation number of -1. To balance the two Cl atoms (-2 total), Ba must be +2.

Give the oxidation number of the indicated atoms/ion.

N in NO₂⁻

• +3

• +4

• +2

• +5

Answer explanation

In NO₂⁻, the overall charge is -1. Oxygen has an oxidation number of -2 (2 oxygens contribute -4). To balance this, nitrogen must have an oxidation number of +3, making the total charge -1.

Give the oxidation number of the indicated atoms/ion.

S in Al₂S₃

• -2

• +2

• 0

• +3

Answer explanation

In Al₂S₃, aluminum (Al) has an oxidation number of +3. To balance the charge, sulfur (S) must have an oxidation number of -2. Therefore, the oxidation number of S in Al₂S₃ is -2.

Give the oxidation number of the indicated atoms/ion.

S in HSO₄⁻

• +4

• +2

• 0

• +6

Answer explanation

In HSO₄⁻, the overall charge is -1. The four oxygen atoms contribute -8 (4 x -2), and hydrogen contributes +1. To balance, sulfur must have an oxidation number of +6, making the correct answer +6.