Why the copper is able to replace the silver, but the reverse reaction will not result in a replacement reaction?

Copper is more reactive and higher in the activity series

Explanation:

Copper is able to replace the silver in a replacement reaction because it is more reactive and higher in the activity series.

Substances or ions that are higher in the activity series are typically more reactive than those ones below them.

In like manner, they are able to replace the lowers ones in a chemical reaction due to their higher reactivity potential.

A less reactive element and a lower one in the activity series cannot displace a higher one in the series.

i believe it is-

d.) gravity pulled particles of dust and gas together to form planets.