Correct Option: A

Malonate is a powerful inhibitor of cellular respiration, because it binds to the active site of succinate dehydrogenase in the citric acid cycle but does not react. It thereby competes with succinate, since it does not have the -CH₂-CH₂- group (as in succinate which is required for dehydrogenation). For the oxidative phosphorylation reaction, malonate is an inhibitor for complex II which again contains succinate dehydrogenase.