Which one of the following represents the correct order of electron releasing tendency of metals?
- (a)Zn > Cu > Ag
- (b)Ag > Cu > Zn
- (c)Cu > Zn > Ag
- (d)Cu > Ag > Zn
Correct — A, Zn > Cu > Ag. Electron-releasing tendency is the ease with which a metal loses electrons (is oxidised), and it is ranked by the reactivity/electrochemical series: the more reactive the metal, the more readily it gives up electrons. Zinc (standard electrode potential -0.76 V) is more reactive than copper (+0.34 V), which is more reactive than silver (+0.80 V). So the descending order of electron-releasing tendency is Zn > Cu > Ag - a zinc atom parts with its electrons far more easily than silver, which is exactly why zinc displaces copper, and copper displaces silver, from their salt solutions.
- (b)Ag > Cu > Zn — The exact reverse of the truth. Silver is a noble, unreactive metal that clings to its electrons; it has the LEAST electron-releasing tendency, not the greatest. This is the order of nobility (resistance to losing electrons), not of reactivity.
- (c)Cu > Zn > Ag — Wrongly places copper above zinc. Zinc is the more reactive metal - it displaces copper from copper sulphate solution (the blue colour fades and reddish copper deposits), proving zinc releases electrons more readily than copper.
- (d)Cu > Ag > Zn — Wrong twice over - it makes copper the leader (zinc should lead) and pushes reactive zinc to the bottom below noble silver. Of the three, zinc is the most reactive and silver the least.
The reactivity (activity) series, and the related electrochemical series, ranks metals by how readily they lose electrons and get oxidised. A metal higher in the series has a more negative standard electrode potential and is a stronger reducing agent. Zinc sits above copper, which sits above silver.
Read 'electron-releasing tendency' as 'reactivity / reducing power'. The most reactive metal loses electrons most easily. Zinc is more reactive than copper, and copper more reactive than silver, so the order must fall Zn > Cu > Ag. The displacement rule confirms it: a more reactive metal kicks a less reactive one out of its salt solution.
- Reactivity (activity) series, high to low: K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au.
- A more reactive metal displaces a less reactive one from its salt solution (e.g. Zn displaces Cu from CuSO4).
- Standard electrode potentials: Zn2+/Zn = -0.76 V, Cu2+/Cu = +0.34 V, Ag+/Ag = +0.80 V; a more negative value means a stronger electron donor.
- Electron-releasing tendency = reducing power; the metal that is oxidised most easily is the strongest reducing agent.
The more negative the electrode potential, the more readily the metal gives up its electrons.
- Confusing the reactivity order with the reverse 'nobility' order (gold and silver are least reactive).
- Assuming a costlier or denser metal is more reactive - reactivity is about losing electrons, not price or density.
Metal reactivity is asked as an ordering ('correct increasing/decreasing order') or as 'which metal displaces which' - memorise the activity series.
No directly related past PYQ was found.
- practice — not a real PYQ
Which one of the following metals will displace copper from copper sulphate solution?
- (a)Silver
- (b)Gold
- (c)Zinc
- (d)Mercury
Answer(c) Zinc - zinc is more reactive than copper, so it displaces it from solution.
- practice — not a real PYQ
In the reactivity series, which one of the following is the least reactive metal?
- (a)Zinc
- (b)Iron
- (c)Gold
- (d)Aluminium
Answer(c) Gold - noble metals like gold and silver resist losing electrons.