Answer
See answer below.
Work Step by Step
a) As: +3 in $As_2S_3$, +5 in $H_3AsO_4$
S: -2 in $As_2S_3$, 0 in $S$
N: +5 in $HNO_3$, +2 in $NO$
b) In 100 g of the compound:
As: $16.199\ g/74.9216\ g/mol=0.216\ mol$
Ag: $69.946\ g/107.8682\ g/mol=0.649\ mol$
O: $13.855\ g/15.999\ g/mol=0.866\ mol$
Dividing by the smallest one:
Ag: $0.649/0.216=3.00$
O: $0.866/0.216=4.00$
Hence the empirical formula is:
$Ag_3AsO_4$
