conc.HNO3

Since conc. nitric acid is an oxidizing agent and iron(II) ion is a reducing agent, redox reaction occurs. The conc. nitric acid is reduced to brown nitrogen dioxide gas, while the pale green iron(II) ion is oxidized to yellowish brown iron(III) ions.
Fe2+(aq) + 2H+(aq) + NO3-(aq) → Fe3+(aq) + H2O(l) + NO2(g)

If iron(II) sulphate solution is used, the water in the solution will dilute the conc. nitric acid to moderately concentrated nitric acid or dilute nitric acid. Therefore, the reaction gives colourless nitrogen monoxide gas instead.
3Fe2+(aq) + 4H+(aq) + NO3-(aq) → 3Fe3+(aq) + 2H2O(l) + NO(g)

yes
Fe2+ ---------> Fe3+ + e-
2H+ + NO3- + e- --------> NO2 + H2O

Fe2+ + 2H+ + NO3- -------> NO2 + H2O + Fe3+

hno3+Feso4=h2so4 +fe(no3)2