Question

What is meant by
(a) $2{\text{H}}\,and{\text{ }}{{\text{H}}_2}$
(b) ${{\text{H}}_2}{\text{O }}and{\text{ 3}}{{\text{H}}_2}{\text{O}}?$

Answer 1

A molecule is a chemically bound group of two or more atoms that are electrically neutral. Molecules differ from ions in that they do not have an electrical charge. In quantum mechanics, organic chemistry, and biochemistry, the distinction between ions and molecules is frequently omitted, and polyatomic ions are referred to as molecules.

Complete answer:
Atoms:
The smallest unit of substance is an atom. It is made up of electrons, protons, and neutrons, among other particles. Although there are a few more interesting subatomic particle terms, those are the three most notable. Neutrons, as their name implies, have no electric charge. The charge of protons is positive. Electrons are charged negatively. Atomic nuclei contain protons and neutrons, while electrons orbit the nucleus.
Molecules:
This is when things start to get interesting. A molecule is made up of atoms that are held together by chemical bonds. Although each atom is a distinct individual, a molecule is formed as certain atoms come together. It could be the same molecule, such as two oxygen atoms bound together (${O_2}$), or it could be separate atoms, such as water (${H_2}O$). The molecule ozone is formed when three oxygen atoms bond together (${O_3}$).
Molecules, too, can become complicated. Acetone, for example, is made up of carbon, hydrogen, and oxygen. As a result, the chemical formula is $C{H_3}COC{H_3}$.
In $2{\text{H}}\,and{\text{ }}{{\text{H}}_2}$
2H refers to the two atoms of hydrogen
Where as
${{\text{H}}_2}$ refers to one molecule of hydrogen gas
Here, In ${{\text{H}}_2}{\text{O }}and{\text{ 3}}{{\text{H}}_2}{\text{O}}$
${{\text{H}}_2}O$ refers to one molecule of water
whereas
${\text{3}}{{\text{H}}_2}O$ refers to three molecule of water

Note:
Water is an inorganic, translucent, tasteless, odourless, and almost colourless chemical element that is the primary component of the Earth's hydrosphere and other recognised living organisms' fluids (in which it acts as a solvent). Even if it contains no calories or organic nutrients, it is essential for all recognised ways of life. Its chemical formula is ${{\text{H}}_2}O$, which means that each of its molecules is made up of one oxygen and two hydrogen atoms that are joined together by covalent bonds.