Which type of pesticide is used to combat organisms like bacillus, coccus, and spirillum?

The correct choice is C, bactericide, because these substances are specifically formulated to target and kill bacteria, which include the types mentioned in the question: bacillus, coccus, and spirillum. Bactericides work by disrupting essential biological processes in bacterial cells or by damaging their cell structures, leading to cell death.

Acaricides are designed to control mites and ticks, not bacteria. Insecticides are focused on insect pests, targeting their specific biology and physiology. Molluscicides, on the other hand, are used to manage mollusks, such as snails and slugs, which do not relate to bacterial control. Each of these alternatives has a specific target organism and action mechanism that does not encompass the bacterial classifications presented in the question.