Which of the following reactions are redox reactions?

a. Al (s) + 3Ag + (aq) →Al3 + (aq) + 3Ag (s)

b. SO3 (g) + H2O (l) →H2SO4 (aq)

c. Ba (s) + Cl2 (g) →BaCl2 (s)

d. Mg (s) + Br2 (l) →MgBr2 (s)

Options A, C and D.

Explanation:

Oxidation is the loss of electrons during a reaction by a molecule, atom or ion. It is represented by an increase in the oxidation number.

Reduction is the loss of electrons during a reaction by a molecule, atom or ion. It is represented by a decrease in the oxidation number.

Both processes makes up what we know as Redox (REDuction - OXidation) reactions.

Note: The oxidation number of an element in its ground state is 0.

To identify which reactions are redox, we look out for change in oxidation number of the molecule, atom or ions involved.

A) Al has an increase in oxidation number for 0 (reactant side) to + 3 (product side), Silver moves from + 1 (reactant) to 0 (product side). this means Al was oxidized and Ag + was reduced. This is a redox reaction.

B) All atoms involved retains their oxidation number. S = + 6, O = -2, H = + 1. This is not a redox reaction.

C) Ba has an increase in oxidation number form 0 to + 2, while Cl has a decrease in oxidation number form 0 to - 2. This is a redox reaction.

D) Mg has an increase in oxidation number form 0 to + 2, while Br has a decrease in oxidation number form 0 to - 2. This is a redox reaction.