Chemistry · S and p Block Elements

The white precipitate of silver chloride dissolves in excess of ammonia, hypo solution and NaCN while bromide ions give a cream precipitate of silver bromide so the results can easily be distinguished.

When you add a dilute solution of sodium hydroxide (NaOH) to the white precipitate of silver chloride (AgCl), it does not dissolve or change. AgCl is insoluble in water and dilute NaOH, so there is no reaction between them. 

When you add a dilute solution of lead(II) nitrate (Pb(NO₃)₂) to the white precipitate of silver chloride (AgCl), it also does not dissolve or change. AgCl is not affected by Pb(NO₃)₂, and there is no noticeable reaction between them. 

To differentiate between the white precipitate of AgCl and the off-white precipitate of AgBr, we need a reagent that can selectively dissolve one of them while leaving the other unchanged. One such reagent is a dilute ammonia (NH₃) solution. AgCl is insoluble in dilute ammonia solution, but AgBr is soluble. Therefore, when we add a dilute ammonia solution to a mixture of AgCl and AgBr precipitates, only the AgBr precipitate will dissolve, leaving the AgCl precipitate unchanged.

So, the correct answer is C) Dilute solution of NH₃.

Adding a dilute solution of iron(III) chloride (FeCl₃) to the white precipitate of silver chloride (AgCl) does not result in any observable reaction. AgCl remains unchanged in the presence of FeCl₃.