Question

When a zinc rod is directly placed in copper sulphate solution?
(A) The blue colored of the solution starts intensifying
(B) The blue coloured remains electrically neutral
(C) The temperature of the solution falls
(D)The weight of zinc rod starts increasing

Answer 1

If we compare the reactivities of copper and zinc, zinc is more reactive than copper. So, copper seems to get replaced by zinc.

Complete step by step answer:
Reactivity series is the series of metals in order of reactivity from highest to lowest. It is in general, used to determine the products of single displacement reactions.

As zinc is more reactive than copper, zinc will displace copper from its solution and will start forming zinc sulphate solution.
The chemical reaction can be:
$Zn + CuS{O_4} \to ZnS{O_4} + Cu$

Number of changes can be seen when zinc rod is placed directly into the solution containing copper sulphate:
The blue color of the solution will eventually fade and disappear after sometime.
Moreover, the weight of the zinc rod will start increasing.
The reason behind all these factors is the displacement reaction. Placing a Zinc rod in a $CuS{O_4}$ solution will undergo a reaction according to which Zn will dissolve because it reduces the $C{u^{2 + }}$ ions to the elemental metal. Due to which, the blue color will fade away and the copper metal will get deposited.

Hence, the weight of the Zn rod starts increasing is the correct statement as it will have to experience the deposition of copper on it.

Hence, the correct option is (D) .

Note:
Displacement reactions are based on the reactivity series. These reactions follow the principle that whichever metal comes first tends to displace the other metal of the reactivity series present in the reaction.