Aluminium,zinc and magnesium can react with dilute hydrochloric acid to give out hydrogen gas.

Introduction:
In order to determine which metal will react with dilute hydrochloric acid to produce hydrogen gas, we need to consider the reactivity series of metals. The reactivity series is a list of metals arranged in order of their reactivity, with the most reactive metal at the top and the least reactive metal at the bottom.

Reactivity series of metals:
The reactivity series of metals can be summarized as follows:
1. Potassium (K)
2. Sodium (Na)
3. Calcium (Ca)
4. Magnesium (Mg)
5. Aluminum (Al)
6. Zinc (Zn)
7. Iron (Fe)
8. Tin (Sn)
9. Lead (Pb)
10. Hydrogen (H)
11. Copper (Cu)
12. Silver (Ag)
13. Gold (Au)

Explanation:
When a metal reacts with hydrochloric acid, it displaces hydrogen from the acid, resulting in the formation of the corresponding metal chloride and hydrogen gas. The reactivity of the metal determines the extent of the reaction. Metals higher in the reactivity series are more likely to react with hydrochloric acid to produce hydrogen gas.

The metal that will react with dilute hydrochloric acid:
Based on the reactivity series, the metal that will react with dilute hydrochloric acid to give out hydrogen gas is magnesium (Mg). Magnesium is more reactive than hydrogen and is located above it in the reactivity series.

Reaction between magnesium and hydrochloric acid:
When magnesium reacts with dilute hydrochloric acid, the following reaction takes place:
Mg + 2HCl → MgCl2 + H2

The magnesium displaces hydrogen from hydrochloric acid, resulting in the formation of magnesium chloride and hydrogen gas. The hydrogen gas is released as bubbles.

Observations:
During the reaction between magnesium and hydrochloric acid, you would observe the following:
1. Effervescence: The formation of bubbles indicates the evolution of hydrogen gas.
2. Fizzing: The reaction between magnesium and hydrochloric acid may produce a fizzing sound due to the release of hydrogen gas.
3. Temperature rise: The reaction is exothermic, which means it releases heat, leading to a rise in temperature.

Conclusion:
Based on the reactivity series, magnesium is the metal that will react with dilute hydrochloric acid to give out hydrogen gas. The reaction between magnesium and hydrochloric acid is represented by the equation: Mg + 2HCl → MgCl2 + H2.