Displacement of Hydrogen from Cold Water by Alkali Metals

The correct answer to the given question is option C: all alkali metals. Alkali metals are a group of elements that belong to Group 1 of the periodic table. This group includes lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Alkali metals have a single valence electron in their outermost energy level, which makes them highly reactive and capable of displacing hydrogen from cold water.

Here is a detailed explanation of why alkali metals can displace hydrogen from cold water:

1. Reactivity of Alkali Metals:
All alkali metals have a strong tendency to lose their single valence electron to achieve a stable electron configuration. This electron loss results in the formation of a positively charged ion (cation). As a result, alkali metals exhibit high reactivity, especially towards water.

2. Reaction with Water:
When alkali metals come into contact with cold water, they react vigorously to produce metal hydroxide and hydrogen gas. The general equation for this reaction is as follows:
2M + 2H2O → 2MOH + H2
where M represents an alkali metal.

3. Formation of Metal Hydroxide:
During the reaction with water, alkali metals form metal hydroxides. For example, sodium (Na) reacts with cold water to produce sodium hydroxide (NaOH).

4. Liberation of Hydrogen Gas:
As a result of the reaction, hydrogen gas (H2) is liberated. This is because alkali metals have a higher affinity for oxygen than hydrogen. Therefore, they displace hydrogen from water to form metal hydroxides.

5. Increasing Reactivity down the Group:
The reactivity of alkali metals increases as we move down the group from lithium to francium. This is due to the increase in atomic size and the ease of losing the single valence electron. Hence, the higher the position of the alkali metal in Group 1, the more vigorously it reacts with water.

In conclusion, alkali metals are capable of displacing hydrogen from cold water due to their high reactivity and tendency to lose their valence electron. This reaction results in the formation of metal hydroxide and the liberation of hydrogen gas.