what is the valency of gold, silver and lead and can you explai how we can find the valency of a compound like NH4, SO2, CO3 etc.
As far as you ask for valencies of elements then, these elements have variable valencies.
valency of gold = 1,3 depending on compound (most common 3)
valency of silver = 1,3 depending on compound(most common 1)
and valency of lead = 2, 4 depending on compound(most common 2)
But, the neutral compounds can not have valencies however elements or ion could have valencies. so we could not determine valencies of the compounds given.