Samples of four metals A, B, C and D are taken and were added to the following solutions one by one. The results obtained have been tabulated as follows :

Solution to which metal is added

Metal	Iron (II) sulphate	Copper (II) sulphate	Zinc sulphate	Silver nitrate
A	No reaction	Displacement	-----	-----
B	Displacement	-----	No reaction	-----
C	No reaction	No reaction	No reaction	Displacement
D	No reaction	No reaction	No reaction	No reaction

Use the table given above to answer the following questions:

(a) Which is the most reactive metal ?

(b) What would you observe when B is added to solution of copper (II) sulphate ?

(c) Arrange the metals A, B, C and D in order of increasing reactivity.

(a) B is the most reactive metal.
Reason — B displaces iron from iron (II) sulphate solution, showing that B is more reactive than iron. It does not displace zinc from zinc sulphate solution, so it is less reactive than zinc. Among the given metals A, B, C and D, metal B is the most reactive.

(b) The blue colour of copper (II) sulphate solution will fade, and a reddish-brown deposit of copper will be formed.
Reason — Since B is more reactive than iron, it is also more reactive than copper. Hence, it will displace copper from copper (II) sulphate solution.

(c) D < C < A < B
Reason — A metal displaces another metal from its salt solution only if it is more reactive than that metal.

• B displaces iron from iron (II) sulphate, so B is more reactive than iron.
• A displaces copper from copper (II) sulphate but does not displace iron from iron (II) sulphate, so A is less reactive than B.
• C displaces silver from silver nitrate but does not displace copper from copper (II) sulphate, so C is less reactive than A.
• D does not displace silver from silver nitrate, so D is the least reactive.

Hence, the increasing order of reactivity is:
D < C < A < B