Animated Solution for Chemistry - s and p-Block Elements: The metal that gives hydrogen gas upon treatment with both acid as well as base is

Amphoteric Metals Explained

In the fascinating world of inorganic chemistry, metals usually follow a strict set of rules. Most active metals love to react with acids to release hydrogen gas, but they completely ignore bases. However, there is a special rebel group of metals that break this rule. These are known as amphoteric metals.

Amphoteric metals have a unique dual personality. They can act like typical metals when placed in an acid, but they can also act somewhat like non-metals when placed in a strong base. In both scenarios, they successfully displace hydrogen to release $H_2$ gas.

Let's look at the metals provided in our question: Magnesium, Mercury, Zinc, and Iron.

Magnesium ($Mg$) and Iron ($Fe$) are classic active metals. If you drop them in dilute hydrochloric acid, they will vigorously bubble and release hydrogen gas. But if you drop them in sodium hydroxide, absolutely nothing happens. They do not react with bases.

Mercury ($Hg$) is a noble-like metal. It sits below hydrogen in the reactivity series. This means it is too weak to displace hydrogen from dilute acids, let alone bases. It remains unreactive in both.

This leaves us with Zinc ($Zn$), which is one of the most famous amphoteric metals.

Imagine dropping shiny zinc granules into a test tube filled with dilute hydrochloric acid ($HCl$). Almost immediately, you will see brisk effervescence. The zinc atoms are actively displacing the hydrogen ions from the acid.

The chemical equation for this single displacement reaction is:

Here, zinc forms aqueous zinc chloride ($ZnC{l}_2$), and hydrogen gas escapes as bubbles.

Now, let's switch things up. What happens if we place zinc in a strong alkali, like dilute sodium hydroxide ($NaOH$)? Because zinc is amphoteric, it doesn't just sit there. It reacts!

In this basic environment, zinc forms a complex soluble salt called sodium zincate, and once again, hydrogen gas is liberated.

The chemical equation for this reaction is:

Notice the formation of the zincate anion ($Zn{O}_2^{2-}$). This is a crucial detail often tested in exams.

Since Zinc is the only metal among the choices that reacts with both an acid and a base to produce hydrogen gas, it is the correct answer.

Pro Tip: Always remember the other common amphoteric metals for your exams: Aluminum ($Al$), Beryllium ($Be$), Tin ($Sn$), and Lead ($Pb$). They all share this incredible dual reactivity!