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Which of the following reactions will not occur $ ? $ Why not $ ? $
(A) $ MgS{O_4}(aq) + Cu(s)\, \to \,CuS{O_4}(aq) + Mg(s) $
(B) $ CuS{O_4}(aq) + Fe(s)\, \to \,FeS{O_4} + Cu(s) $
(C) $ MgS{O_4}(aq) + Fe(s)\, \to \,FeS{O_4}(aq) + Mg(s) $

Last updated date: 17th Mar 2023
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Hint : To solve the question, we must know what type of reaction is taking place here. It is a displacement reaction. Displacement reaction is a chemical reaction in which one element is displaced by another in a compound. A more reactive metal displaces a less reactive metal from its salt.

Complete Step By Step Answer:
In a displacement reaction, a more reactive metal displaces a less reactive metal from its salt solution. Reactivity of metals is explained by the reactivity series. It is the arrangement of metals in the order of their reactivity- from highest to lowest. Metals on the top of the reactivity series can displace the metals that are below them from their salt. Potassium (K) is placed on the top of the series and hence it is the most reactive metal. Metals like K, Na, Ca, Mg ,Al, C, Zn,Fe,Sn, Pb are very reactive, whereas Cu, Ag, Au, Pt are relatively unreactive.
In reaction (A) Cu displaces Mg from its salt which is not possible because Cu is less reactive than Mg.
Reaction (B) shows the displacement of Cu from its salt by Fe. Since Fe is more reactive than Cu, the above reaction is possible.
In the reactivity series, Mg is placed above Fe and therefore Fe cannot displace Mg from its salt solution. Therefore, reaction (C) is also not possible.
Thus, reactions (A) and (C) cannot occur since, a less reactive metal cannot displace a more reactive metal.

Note :
Reactivity of metals is based on its outer electronic configuration, size etc. More the tendency to lose its electrons, more will be the reactivity of the metal. Reducing power of metal decreases as we go from top to bottom.
Hydrogen is the only non metal in the reactivity series and is placed in the middle. Metals placed above hydrogen are very reactive and that placed below are very less reactive.