The reaction given below is catalysed by oxidoreductases between two substrates $A$ and $A'$. Complete the reaction: $A \text{ reduced} + A' \text{ oxidised} \longrightarrow$ ?

(A) Oxidoreductases are enzymes that catalyse oxidoreduction between two substrates $S$ and $S'$ by transferring electrons. The general reaction is: $S \text{ reduced} + S' \text{ oxidised} \longrightarrow S \text{ oxidised} + S' \text{ reduced}$.
In the given case, substrate $A$ is in a reduced state and $A'$ is in an oxidised state. During the reaction, $A$ donates electrons (acts as an electron donor) and becomes oxidised, while $A'$ accepts electrons (acts as an electron acceptor) and becomes reduced.
Therefore, the complete reaction is: $A \text{ reduced} + A' \text{ oxidised} \longrightarrow A \text{ oxidised} + A' \text{ reduced}$.