Chemistry · Redox Equilibrium · NEET
It is both. Zinc is more reactive than copper, so zinc displaces copper from copper sulphate - that makes it a displacement reaction. It is also redox because Zn goes from 0 to +2 (oxidised, loses electrons) and Cu goes from +2 to 0 (reduced, gains electrons). Every metal displacement reaction is a redox reaction, because oxidation states change.
Use the reactivity series (activity series). A metal higher in the series (more reactive, more electropositive) displaces any metal below it from its salt. Shortcut with electrode potentials: the metal with the MORE NEGATIVE standard reduction potential is the stronger reducing agent and does the displacing. Example: Zn (E° = -0.76 V) is above Cu (E° = +0.34 V), so Zn displaces Cu, but Cu cannot displace Zn.
In METAL displacement, one metal pushes out another metal from its salt, e.g. Cr2O3 + 2Al -> Al2O3 + 2Cr. In HYDROGEN displacement, a reactive metal pushes hydrogen out of an acid or water, releasing H2 gas, e.g. Fe + 2HCl -> FeCl2 + H2. NEET often lists both as options in one question - look at what got displaced: a metal or hydrogen gas.
Oxidising power of halogens decreases down the group: F2 > Cl2 > Br2 > I2. A halogen only displaces a halide ion that is BELOW it. So Cl2 (stronger oxidiser) takes electrons from Br- and I-, forming Br2 and I2. But Br2 is weaker than Cl2, so it cannot pull electrons from Cl- ions. The stronger oxidiser always displaces the weaker one, never the reverse.
Yes. In Cr2O3 + 2Al -> Al2O3 + 2Cr, aluminium is more reactive than chromium, so Al displaces Cr from its oxide. This is the classic NEET metal displacement example (thermite reaction). Al is oxidised (0 to +3) and Cr is reduced (+3 to 0). It was the correct answer in NEET 2021.
Metal and non-metal displacement reactions ARE redox reactions - a free element (oxidation state 0) becomes an ion, and an ion becomes a free element, so oxidation states change. But be careful: DOUBLE displacement (like BaCl2 + Na2SO4 -> BaSO4 + 2NaCl) is NOT redox, because no oxidation state changes there. NEET tests this trap.
Which of the following reactions is a metal displacement reaction?
Which reaction is NOT a redox reaction?
The standard electrode potential (E°) values of Al3+/Al, Ag+/Ag, K+/K and Cr3+/Cr are -1.66 V, +0.80 V, -2.93 V and -0.74 V respectively. The correct decreasing order of reducing power of the metals is
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A displacement reaction is one where a more reactive element takes the place of a less reactive element in a compound. The more reactive metal or non-metal 'kicks out' the weaker one, and it is always a redox reaction because a free element becomes an ion and an ion becomes a free element.
Metal displacement (a more reactive metal displaces a less reactive metal from its salt or oxide, e.g. Zn + CuSO4 -> ZnSO4 + Cu) and non-metal displacement (a more reactive non-metal displaces a weaker one, e.g. Cl2 + 2KBr -> 2KCl + Br2, or H2 displaced by a metal from acid/water).
A metal with a more negative standard reduction potential is a stronger reducing agent and will displace a metal with a more positive potential from its salt. For halogens, a higher standard reduction potential means a stronger oxidiser, so it displaces the halide below it (F2 > Cl2 > Br2 > I2).
No. In hydrogen displacement a reactive metal frees H2 gas from an acid or water (Fe + 2HCl -> FeCl2 + H2). In metal displacement one metal replaces another metal. Both are redox and both are 'single displacement', but NEET keeps them as separate answer choices.
In single displacement a neutral element (oxidation state 0) turns into an ion and an ion turns into a neutral element, so oxidation states must change - that is redox. In double displacement only ion partners swap (like BaCl2 + Na2SO4), no oxidation state changes, so it is not redox.
