Question

On reaction with dilute HCl, which of the following pair of metals will evolve hydrogen gas?

• A. Copper and zinc
• B. Copper and iron
• C. Silver and magnesium
• D. Magnesium and aluminium

Hint:

Metals above hydrogen in reactivity series evolve H$_2$ with acids.

Answer 1

The Correct Option is D

To determine which pair of metals will evolve hydrogen gas when reacted with dilute hydrochloric acid (HCl), we need to understand the reactivity series of metals. The reactivity series is a list of metals arranged in order of decreasing reactivity. Metals placed higher in the series can displace hydrogen from acids, leading to the evolution of hydrogen gas.

The relevant reactivity series for common metals is as follows:

1. Potassium (K)
2. Sodium (Na)
3. Calcium (Ca)
4. Magnesium (Mg)
5. Aluminium (Al)
6. Zinc (Zn)
7. Iron (Fe)
8. Lead (Pb)
9. Hydrogen (H)
10. Copper (Cu)
11. Silver (Ag)

Only metals that are above hydrogen in the reactivity series can displace hydrogen from an acid like dilute HCl. Let's evaluate each pair of metals given in the options:

• Copper and zinc: Zinc is above hydrogen, but copper is not. So, only zinc will evolve hydrogen gas.
• Copper and iron: Iron is above hydrogen, but copper is not. So, only iron will evolve hydrogen gas.
• Silver and magnesium: Magnesium is above hydrogen, but silver is not. So, only magnesium will evolve hydrogen gas.
• Magnesium and aluminium: Both magnesium and aluminium are above hydrogen in the reactivity series, so both will evolve hydrogen gas.

Thus, the correct answer is the pair "Magnesium and aluminium," as both metals react with dilute HCl to release hydrogen gas.