a mutagen is\n○ a living thing that has undergone a mutation.\n○ an agent that causes a mutation in dna.\n○…

a mutagen is\n○ a living thing that has undergone a mutation.\n○ an agent that causes a mutation in dna.\n○ a mutation that has affected one gene.\n○ any chemical that can poison living cells.

a mutagen is\n○ a living thing that has undergone a mutation.\n○ an agent that causes a mutation in dna.\n○ a mutation that has affected one gene.\n○ any chemical that can poison living cells.

Answer

Brief Explanations:

A mutagen is defined as an agent (which can be chemical, physical like radiation, etc.) that induces changes in the DNA sequence, leading to mutations. The other options do not correctly define a mutagen. A living thing that has undergone a mutation is a mutant, not a mutagen. A mutation affecting one gene is just a type of mutation, not a mutagen. And a chemical that can poison living cells is not necessarily a mutagen as its primary action may not be to cause DNA - mutations.

Answer:

an agent that causes a mutation in DNA.