Two compounds of iron are given.
`FeSo_4, Fe_2(SO_4)_3`
(The oxidation state of `SO_4 -2`)
a. Identify the compound in which iron shows +2 oxidation state.
b. Which of these compound posses `Fe^3+` ions.
c. write the subshell electronic configuration of `Fe^3+` ions
d. Give reason for the various oxidation states of transition elements.

Explanation

`a. FeSO_4`
`b. Fe_2 (SO_4)_3`
`c. Fe_3+ - 1s^2 2s^2 2p^6 3s^2 3p^6 3d^s`
d. The energy of electrons in the outermost s subshell and the penulimate d subshell has almost the same energy. Hence under suitable conditions the elctrons in the d subshell also take part in chemical reactions.