Question

Why during the preparation of ammonia the flask in which it is being prepared is tilted?

Answer 1

I think you are asking about this process of preparing ammonia. In this reaction the water will form as a product
Ca(OH)2+2NH4Cl --> CaCl2+2NH3 + 2H2O
In this reaction if we keep the RB flask in upward position the water evaporated will condense and comeback as water again. This will lead to increase in pressure (Because already the ammonia gas is present in the flask). So to remove the water from the RB flask we are keeping it in tilted position.