Antonym of Taxing:

The word Taxing means physically or mentally demanding, difficult, or burdensome. Therefore, its antonym, a word with the opposite meaning, is Clear, implying something that is easy, straightforward, or not demanding.

• Challenging is a synonym, meaning testing one's abilities; demanding.
• Strenuous is also a synonym, meaning requiring or using great exertion.
• Exhausting is another synonym, meaning making one feel very tired; extremely demanding.

All the distractors describe something difficult or demanding, whereas 'clear' suggests ease and simplicity, making it the correct antonym.