Well, I'm not sure about that answer key, to be honest.
Tin can have two oxidation states, +2 and +4.
In tin (II) selenide, or tin selenide (this is more of a common name), the tin atom has a +2 oxidation state and the compound has this formula :
In tin (IV) selenide, the tin atom has a +4 oxidation state, the compound's formula being
I think that either the formula given is wrong, i.e. it should be
Since that option is not available, an alternative name for tin (II) selenide is actually stannous selenide, which would make the correct answer
(3) stannous selenide