The correct answer is option 2, Copper.

When a metal reacts with a dilute acid, it can displace hydrogen gas from the acid if it is more reactive than hydrogen. This is because metals that are more reactive have a greater tendency to lose electrons and form positive ions, which allows them to displace hydrogen from the acid.

Zinc, magnesium, and iron are all more reactive than hydrogen, so they can displace hydrogen gas from a dilute acid. However, copper is less reactive than hydrogen, so it cannot displace hydrogen gas from a dilute acid.

It is important to note that the reactivity series of metals determines their ability to displace hydrogen gas from acids. Metals higher up in the reactivity series, such as zinc and magnesium, can displace hydrogen from a wider range of acids compared to metals lower down in the series, such as copper and silver.

In summary, copper cannot displace hydrogen gas from a dilute acid because it is less reactive than hydrogen.