The hydrochloric bottles left out in the laboratorywith time become covered with white powder suggest a possible composition for this powder why do ammonia bottles bacome less covered than the HCl?

Answer 1

The powder on your HCl bottles might well be NH4Cl, as you seemingly assumed already.

The reason why the ammonia bottles become less covered is hard to guess, but maybe it's simple: When the airborne concentration of ammonia is higher than the concentration of HCl, the HCl is precipitated by the ammonia right away after it left the bottle. Thus, it won't reach the ammonia bottles.

Of course, there could be different reasons, e.g., different crystallisation surfaces of the bottles, air currents and directions, or just the kinds and numbers of the particular bottles in the lab. Though, the latter could also entail a higher ammonia concentration.

Answer 2

The white powder on the hydrochloric acid bottles is likely sodium chloride (table salt) formed when HCl vapors react with moisture in the air. Ammonia bottles become less covered because ammonia gas is less reactive with moisture in the air compared to hydrochloric acid, resulting in less formation of solid products on the bottle surfaces.