1. Complete the following sentences: (a) Oxidation is a gain of electrons OR an increase in oxidation state
(b) Reduction is a loss of electrons OR a decrease in oxidation state
(c) Redox reactions involve a transfer of electrons from the element being to the element being .

2. Complete the rules for assigning oxidation numbers by filling in the missing words.
(1) The oxidation number of an element is .
(2) The oxidation number of a monatomic ion is equal to the of the ion.
(3) In a polyatomic ion, the oxidation numbers of all the atoms in the ion add up to the
of the ion.
(4) In a compound, the sum of all the oxidation numbers of the atoms is
(5) The oxidation number of oxygen in its ions and compounds is always
except in where it is -1.
(6) The oxidation number of hydrogen in its ions and compounds is always
(7) The oxidation number of elements in compounds is often the same as their if they were an ion

3. Give the oxidation number of the bold species in each of the following substances.

H2O S8 H2O2
AlCl3 O3 Fe2O3
MnO2 Cu KMnO4

4. Give the oxidation number of the bold species in each of the following substances.

Br- S2O32- NH4+
H2S MnO4- Cr3+
O22- Cr2O72- I-
C2O42- NO3- OCl-
SO42- MnO2 SO2
.

5. State the oxidation number of the underlined element in each of the following species.
(a) HCl (j) FeSO4
(b) CO2 (k) Fe2(CO3)3
(c) SO32- (l) KMnO4
(d) CO (m) MnI2
(e) KI (n) CaO
(f) H2O2 (o) Cr2O72-
(g) Cr(NO3)3 (p) HSO3-
(h) Br2 (q) ZnO
(i) H2SO4 (r) H2O

6. State whether each of the following reactions is an oxidation or a reduction reaction. Justify.
(a) O2- → O2
(b) I2 → I-
(c) Mg2+ → Mg
(d) HSO3- → SO42-
(e) Fe3+ → Fe2+
(f) Br2 → Br-
(g) Cr2O72- → Cr3+
(h) MnO4- → Mn2+
(i) Cl2 → Cl-
(j) H+ → H2