Explanation:

- The phrase "obsession with one particular thing" refers to a focused and often intense preoccupation with a specific subject or activity.

- Option 1: Hypomania

- Refers to a mood state characterized by persistent disinhibition and mood elevation that is not as extreme as mania. It doesn't necessarily involve obsession with one thing.

- Option 2: Monomania

- Defined as an obsession with a single thought or idea, particularly excluding everything else.

- Monomania is the correct answer for an obsession with one particular thing.

- Option 3: Insomnia

- Describes a sleep disorder where people have trouble sleeping. It is unrelated to singular obsessions.

- Option 4: Pyromania

- Refers to an irresistible impulse to start fires. Though an obsession, it's specific to fire-setting.