Answer: The true statement is iron can reduce [tex]Au^+(aq)[/tex] to gold metal
Explanation:
Single displacement reaction is defined as the reaction in which more reactive element displaces a less reactive element from its chemical reaction.
The reactivity of metal is determined by a series known as reactivity series. The metals lying above in the series are more reactive than the metals which lie below in the series.
[tex]A+BC\rightarrow AC+B[/tex]
Metal A is more reactive than metal B.
We are given:
Iron can reduce copper, silver can reduce gold, sodium can reduce iron and copper can reduce silver metal.
The increasing order of reactivity thus follows:
[tex]Au<Ag<Cu<Fe<Na[/tex]
where, sodium is most reactive and gold is least reactive
For the given options:
Option 1: Copper cannot easily reduce sodium ion to sodium metal because it is less reactive.
[tex]Cu(s)+Na^+(aq.)\rightarrow \text{ No reaction}[/tex]
Option 2: Iron cant easily reduce gold ion to gold metal because it is more reactive.
[tex]Fe(s)+3Au^+(aq.)\rightarrow Fe^{3+}(aq.)+3Au(s)[/tex]
Option 3: Silver cannot easily reduce iron ion to iron metal because it is less reactive.
[tex]Ag(s)+Fe^{3+}(aq.)\rightarrow \text{ No reaction}[/tex]
Hence, the true statement is iron can reduce [tex]Au^+(aq)[/tex] to gold metal