Question

Four students A, B, C and D noted the initial colour of the solutions in beakers I, II, III and IV. After inserting zinc rods in each solution and leaving it undisturbed for two hours, noted the colour of each solution again.



They recorded their observations in the form of a table given below:

Student	Colour of the solution	I	II	III	IV
A	Initial Final	Colourless Colourless	Colourless Colourless	Light green Colourless	Blue Colourless
B	Initial Final	Colourless Colourless	Light yellow Colourless	Light green Light green	Blue Colourless
C	Initial Final	Colourless Light blue	Colourless Colourless	Light green Colourless	Blue Light blue
D	Initial Final	Light green Colourless	Colourless Colourless	Light green Dark green	Blue Colourless

Which student noted the colour change in all the four beakers correctly?

Answer 1

For I, zinc rod is dipped in aluminum sulphate, but zinc is less reactive than aluminum so, no reaction will take place.
For II, zinc rod is dipped in zinc sulphate, here no reaction will take place as zinc rod is dipped in zinc solution.
For III, zinc rod is dipped in ferrous sulphate, zinc is more reactive than ferrous sulphate. Ferrous sulphate is of light green color which on reaction with zinc gives zinc sulphate which is colorless.
$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{FeSO}}_4\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)+\mathrm{Fe}\left(\mathrm{s}\right)$
For IV, zinc rod is dipped in copper sulphate, zinc is more reactive than Copper sulphate. Copper sulphate is of light blue color which on reaction with zinc gives zinc sulphate which is colorless.
$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)\to {\mathrm{CuSO}}_4\left(\mathrm{aq}\right)+\mathrm{Fe}\left(\mathrm{s}\right)$
So, the observations made by student A are correct.

Hence, the correct answer is option 1.