The reaction for tarnish formation is due to contact with hydrogen sulfide.

$2A{g}_{\left(s\right)}+H_2{S}_{\left(g\right)}\to A{g}_2{S}_{\left(s\right)}+H_{2\left(g\right)}$

and the above tarnish can be removed by using Al metal as

$2Al+3A{g}_{2}S\to A{l}_2{S}_3+6Ag$

The above two reactions appear to be displacement reactions. But ‘Ag’ is less reactive than ‘H’ in the reactivity series. Then what might be the reason?

i) ‘Ag’ can displace ‘H’ under certain conditions even though it is less

reactive

ii) Ag cannot react directly with $H_{2}S$  to displace ‘H’ from it.

iii) ‘Ag’ first oxidized to its oxide and then it reacts with $H_{2}S$  to form

$A{g}_{2}S$

iv) The formation of $A{g}_{2}S$  is possible by a decomposition reaction.