The synonym of Avocation:

To find the synonym of 'Avocation', we must understand its meaning. An 'avocation' is a hobby or minor occupation, something done in addition to one's main job, usually for pleasure.

• B. Hobby: This is the correct synonym. A 'hobby' is an activity done regularly in one's leisure time for pleasure. This perfectly matches the definition of avocation.
• A. Duty: A 'duty' is a moral or legal obligation or responsibility. This is the opposite of an avocation, which is typically voluntary and for enjoyment.
• C. Obligatory: This adjective means required by a legal, moral, or other rule; compulsory. Like 'duty', it implies a requirement rather than a choice for pleasure.
• D. None of these: This is incorrect because 'Hobby' is a direct synonym for 'Avocation'.