In the laboratory preparation of ammonia, the flask is placed in a slanting position so as to

Correct answer: Prevent condensed water from breaking the reaction flask

Explanation: In the lab preparation of ammonia (by heating NH₄Cl with Ca(OH)₂ or NaOH), the flask is placed slanting so that any water vapour that condenses runs to a cooler part of the flask and does not drip back onto the very hot glass. Sudden cooling of the hot region can crack the flask. Tilting prevents this thermal shock.

• Enable proper mixing — Not the purpose.
• Enhance the speed of the reaction — Not primarily affected by the tilt.
• Prevent formation of precipitate — Irrelevant here.