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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?

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Solution

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.
Zn(s)+FeSO4(aq)ā†’ZnSO4(aq)+Fe(s)
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.
Zn(s)+CuSO4(aq)ā†’CuSO4(aq)+Fe(s)
So, the observations made by student A are correct.

Hence, the correct answer is option 1.

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