Fe(s)+Ca(NO₃)₂(aq)⇒no reaction
Further explanation
In voltaic series
Li-K-Ba-Ca-Na-Mg-Al-Mn- (H2O) -Zn-Cr-Fe-Cd-Co-Ni-Sn-Pb- (H) -Cu-Hg-Ag-Pt-Au
The more to the left, the metal is more reactive (easily release electrons) and the stronger reducing agent
The more to the right, the metal is less reactive (harder to release electrons) and the stronger oxidizing agent
So that the element located on the left can push the element on the right in the redox reaction
Reaction
Fe(s)+Ca(NO₃)₂(aq)⇒no reaction
Fe cannot reduce Ca because Ca is more reactive, so the reaction does not occur
On the contrary, this reaction can occur
3Ca(s) + 2Fe(NO₃)₃(aq) = 3Ca(NO₃)₂(aq) + 2Fe(s)