Question

Which substance is oxidized and reduced in the following chemical reaction.
$ZnO + C \to Zn + CO$

Answer 1

When a pair of reactants involves one chemical species getting oxidized and the other getting reduced, it is called a redox reaction. Oxidation can be observed by a simple gain of oxygen atoms or the loss of electrons.

Complete answer:
The reaction between zinc oxide and carbon is a redox reaction that produces zinc metal and carbon monoxide gas.
Oxidation is a process in which a chemical species gains one or more oxygen atoms. This gain is through the formation of a chemical bond and an oxide formation takes place. Reduction is just the opposite of oxidation and is defined as the process by which a chemical species loses its oxygen atoms.
The reaction starts with zinc oxide and results in zinc metal which means that zinc loses its oxygen atoms so as to obtain its stable metallic form. Moreover, zinc being an electropositive element has a positive two oxidation state in zinc oxide but reduces to zero oxidation state.
The reaction starts with carbon in its solid form and results in the formation of carbon monoxide which means that carbon obtains or gains oxygen atoms to form an oxide. Carbon in its native solid state has a zero oxidation state but acquires a positive two oxidation state.
Thus zinc oxide gets reduced and carbon gets oxidized.

Note:
The species that gets oxidized or reduced is always the reactant and never the product. If the reactant is a compound then the element that undergoes a change in oxidation state is said to be oxidized or reduced. Like in the case of zinc oxide, it is actually zinc that undergoes reduction.