Which two reactions are redox reactions?

synthesis and decomposition

combustion and synthesis

combustion and single-replacement

single-replacement and double-replacement

Combustion and single replacement.

Explanation:

The oxidation reduction reactions are called redox reaction. These reactions are take place by gaining or losing the electrons and oxidation state of elements are changed.

Oxidation:

Oxidation involve the removal of electrons and oxidation state of atom of an element is increased.

Reduction:

Reduction involve the gain of electron and oxidation number is decreased.

The combustion and single replacement reactions are always redox.

Consider the following reactions.

Mg + CuSO₄ → Cu + MgSO₄

the oxidation state of copper is changed from + 2 to 0 so copper get reduced.

the oxidation state of Mg is changed from 0 to + 2 so it get oxidized.