Explanation:

- The word "quixotic" describes someone or something exceedingly idealistic, unrealistic, and impractical.

- Option 1: imaginary

- "Imaginary" means existing only in the imagination, not real or practical. It's closer in meaning to quixotic, not an opposite.

- Option 2: fantastic

- "Fantastic" refers to something remarkable or imaginative, often not grounded in reality. It aligns more with "quixotic" rather than opposing it.

- Option 3: mournful

- "Mournful" means full of sorrow, which doesn't relate to quixotic's idealistic but unrealistic nature. It doesn't counteract quixotic.

- Option 4: practical

- "Practical" implies being grounded, realistic, and focused on what is achievable.

- It directly contrasts with quixotic's tendency to dream without considering reality.