The correct order of acidity for the following compounds is

The major product of the following reaction sequence is:

In the following reaction, sequence in aqueous solution, the species X, Y and Z, respectively, are

$${S_2}O_3^{2 - }\buildrel {A{g^ + }} \over \longrightarrow \mathop X\limits_{Clear\,solution} \buildrel {A{g^ + }} \over \longrightarrow \mathop Y\limits_{White\,precipitate} \buildrel {With\,time} \over \longrightarrow \mathop Z\limits_{Black\,precipitate} $$