Question

Consider following sets. Blue colour solution changes to colourless (or fades) in:

• A. I, II, III
• B. I, II
• C. II, III
• D. I, III

Answer 1

The correct option is D I, III

The solution changes colour from blue to colourless because copper ions are reduced to copper metal.
Zinc (with negative $E^0$ value) is stronger reducing agent than copper (with positive $E^0$ value). Hence zinc can displace copper ions from its salt solution.
Magnesium (with negative $E^0$ value) is stronger reducing agent than copper (with positive $E^0$ value). Hence magnesium can displace copper ions from its salt solution.
Silver (with more positive $E^0$ value) is weaker reducing agent than copper (with less positive $E^0$ value). Hence silver cannot displace copper ions from its salt solution.