Agents are termed "infective" when they are capable of which of the following?

Agents are termed "infective" when they have the capability to produce infection in a host. This essentially refers to microorganisms such as bacteria, viruses, fungi, and parasites that can invade the body, multiply, and cause disease. Infective agents can disrupt normal physiological processes and lead to various infections, which can result in symptoms and potentially serious illnesses.

The other options do not describe the characteristic of being infective. For instance, options regarding the quality of not having toxic effects, the inability to open the mouth fully, and a decrease in platelets in circulating blood relate to different aspects of health and physiology but do not define the capacity to cause infection. Thus, the specific definition that focuses on the ability to produce infection aligns directly with the term "infective."