Which type of chemical agent is primarily responsible for causing mutations in living organisms?

A mutagen is a substance that causes changes in the DNA of an organism, leading to mutations. These changes can occur in various ways, such as by altering the structure of DNA or interfering with its replication processes. Mutagens can be physical agents, like radiation, or chemical agents that directly affect genetic material. The significance of mutagens lies in their ability to create variations in genetic sequences, which can result in non-functional or dysfunctional genes.

In contrast, carcinogens are substances that can lead to cancer but are not exclusively defined as agents that cause mutations. While many carcinogens can also act as mutagens by altering DNA, their primary role is associated with the processes that lead to cancer development, which may involve multiple stages beyond initial DNA mutation.

Allergens are substances that trigger allergic reactions in sensitive individuals; they do not typically cause mutations. On the other hand, teratogens are agents that can cause birth defects during the embryonic development stage, primarily affecting growth and development rather than directly inducing genetic mutations.

Thus, the correct answer identifies the specific role of mutagens in causing mutations, distinguishing them from other types of agents that have different health implications.