What noise does hydrogen gas create when a lighted candle is placed close to the opening of the test tube where it is evolved?

Pop

The correct answer is option 2. pop.

When hydrogen gas \((H_2)\) is exposed to a flame, such as that from a lighted candle, it undergoes a rapid combustion reaction. The hydrogen gas reacts with oxygen \((O_2)\) present in the air to form water \((H_2O)\) vapor. This reaction releases a significant amount of energy in the form of heat and light.

The chemical equation for the combustion of hydrogen gas can be represented as follows:

\(2H_2(g) + O_2(g) \longrightarrow 2H_2O(g)\)

In this reaction, two molecules of hydrogen gas react with one molecule of oxygen gas to produce two molecules of water vapor.

When the hydrogen gas in the test tube encounters the flame from the candle, the combustion reaction occurs rapidly. The heat generated by the flame provides the activation energy required to initiate the reaction between hydrogen and oxygen. As a result, the hydrogen gas combusts explosively, producing a sudden release of energy.

The popping sound heard when hydrogen gas ignites is caused by the rapid expansion of gases resulting from the combustion reaction. The force of the expanding gases creates a small explosion, which produces the characteristic pop sound. This sound is a clear indication that hydrogen gas is flammable and can undergo combustion in the presence of a flame.

Overall, the popping sound produced when a lighted candle is placed close to the opening of a test tube containing hydrogen gas is a result of the rapid combustion reaction between hydrogen and oxygen, leading to a small explosion.