Choose the correct antonym of the word Onerous from the options given below:

Option 1: Arduous -> means difficult and requiring great effort; this is actually a synonym of onerous, not an antonym.

Option 2: Opulent -> means wealthy or luxurious; this word is unrelated to the concept of being burdensome.

Option 3: Effortless -> means requiring no effort or easy to do; this is the direct opposite of onerous (burdensome/difficult).

Option 4: Favourable -> means advantageous or positive; while somewhat opposite in tone, it's not the precise antonym.

Hence, Option 3: Effortless -> Onerous means burdensome or requiring considerable effort, so its antonym would be something that requires no effort at all -> correct