Question

What takes place when zinc metal is added to an aqueous solution containing magnesium nitrate and silver nitrate?
$1.Zn$ is oxidised
$2.M{g^{2 + }}$ is reduced
$3.A{g^ + }$ is reduced
$4.$ No reaction takes place
(A) $1$ and $2$ only
(B) $1$ and $3$ only
(C) $1,2$ and $3$ only
(D) $4$ only

Answer 1

In this type of question, we must know about the reactivity series of metals. Because in this reaction zinc metal is added to a solution, so it can displace other metal from its solution and form a new solution. These types of reactions are known as displacement reactions and can be answered on the basis of the reactivity series of metals.

Complete answer:
We first need to know about displacement reaction because in this reaction zinc metal is added to a solution, so it can displace other metal from its solution and form a new solution.
So, displacement reaction is a chemical reaction in which a metal displaces another metal or element from its solution and forms a solution of a new compound.
The stronger (more reactive) metal displaces the weaker (less reactive) metal from its solution to form a new compound. Here comes the role of reactivity series, because through reactivity series we can determine the strength of the metals.
Therefore, reactivity series of metals is given as follows:
$K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au$
Here, we can see that Magnesium is more reactive than zinc, so zinc metal cannot displace magnesium from magnesium nitrate while silver is less reactive than zinc, so zinc metal can displace silver from silver nitrate solution.
Hence, zinc metal will get oxidised from $0 \to + 2$ and silver $(A{g^ + })$ will get reduced as it comes into its elemental state.

Therefore, the correct option is (B) $1$ and $3$ only.

Note:
We should note that when a metal is getting oxidised, then its oxidation state increases such that it becomes more positive while if the metal is getting reduced, then its oxidation state decreases (the oxidation state becomes more negative). Hence, by looking at the change in oxidation state, we can identify the oxidation and reduction process.