Question

When hydrogen and oxygen combine to form water, they form:
(A) an unstable compound
(B) a stable mixture
(C) an unstable mixture
(D) an extremely stable compound

Answer 1

Hint: Hydrogen and oxygen are two gases which combine together to form water, which is a liquid. It is difficult to break water molecules into their components. The gases are also very eager to form water molecules.

Complete answer:
Hydrogen is a chemical element with atomic number $1.$ It is symbolized as “H” in its elemental form. Oxygen is a chemical element with atomic number $8.$ It is symbolized as “O” in its elemental form. Both hydrogen and oxygen exist as diatomic molecules, symbolized as ${H_2}$ and ${O_2}$ respectively. When hydrogen and oxygen combine, they form water $\left( {{H_2}O} \right).$
Both the hydrogen atom and the oxygen atom are unstable on their own. To become stable, the hydrogen atom must contain $2$ electrons in its valence shell, and the oxygen atom must contain $8$ electrons in its valence shell. To fill their valence shell and reach a state of stability, these atoms combine together by forming covalent bonds with each other. This equation represents the formation of water:
$2{H_2} + {O_2} \to 2{H_2}O$
 When water is formed, a large amount of energy is released. This is a sign that the compound formed is highly stable. Therefore, when hydrogen and oxygen combine to form water, they form (D) an extremely stable compound.

Note:
The stability of water molecules lies in the fact that they can form hydrogen bonds. Hydrogen bonding has one of the strongest intermolecular attractive forces in covalent bonding. It is mainly an electrostatic attraction between a hydrogen atom and an electronegative atom or group of atoms. In the case of water, the electronegative atom is oxygen.