A colourless solution of silver nitrate is taken in two test tubes A and B. Metal plates of copper and platinum are dipped into test tubes, A and B, respectively. Content of test tubes:

The reactivity series is a way to group metals according to how reactive they are. On top of the series are the metals that are more reactive. Less reactive metals can be displaced from their salt solution by more reactive metals.

The term "activity series," which refers to the arrangement of metals in decreasing order of their reactivity, is used to describe the metals' reactivity series. Metals quickly give up their electrons to generate cations. Metal oxides are created when they interact with air oxygen. But the reactivity of certain metals to oxygen varies. The metals' reactivity series explains each of these characteristics.
The metals listed in decreasing order of reactivity are

Potassium, sodium, calcium, magnesium, iron, lead, hydrogen, copper, silver, and gold are just a few examples.
Among its characteristics are,

A. Because they can be quickly oxidised, the metals near the top of the reactivity range are powerful reducing agents. Corrosion happens quickly to these metals.

B. As the series goes down, the metals' capacity to reduce declines.

C. As metal reactivity increases, the electropositivity of the components decreases.

D. When interacting with acids, any metals in the activity series above hydrogen can release hydrogen gas.

Metals that are located lower from their salt solutions might be displaced by metals that are present higher on the reactivity series. Due to its lower reactivity than silver in the aforementioned question, gold is the sole element listed below silver. Therefore, it is unable to remove silver from its salt solution.
Since copper is more reactive than silver in test tube A, a displacement reaction occurs, displacing the silver from the silver nitrate solution to create the blue copper nitrate solution. Written as the chemical reaction is:
$\mathrm{Cu}+\mathrm{Ag}{({\mathrm{NO}}_3)}_2\to \mathrm{Cu}{({\mathrm{NO}}_3)}_2+\mathrm{Ag}$

Hence, the correct option is C.