When an alkali-metal reacts with water, which one of the following gases is produced?

When alkali metals (Group 1 elements such as lithium, sodium, and potassium) react with water, they produce a metal hydroxide and hydrogen gas. This is a highly exothermic redox reaction where the metal displaces hydrogen from the water molecule [t4][t9]. The general chemical equation is 2M(s) + 2H2O(l) → 2MOH(aq) + H2(g) [t4][t8]. For metals like sodium and potassium, the reaction is so violent that the evolved hydrogen gas often catches fire, burning with a characteristic flame [c1][t1]. The presence of hydrogen can be confirmed using the 'squeaky pop' test with a burning splint [t8]. While the solution becomes basic due to the formation of hydroxide ions, the primary gas evolved is molecular hydrogen [t6][t10]. Other gases like oxygen, ozone, or hydrogen peroxide are not products of this specific reaction.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Activity 3.10 > p. 43