Question

What is the coordination number of oxygen in ${H_2}O(l)$?

Answer 1

Coordination number is referred to the number of atoms a single atom is touching or is in direct contact with or the number of ions that surrounds an ion of the opposite charge within a specific arrangement.

Complete answer:
For molecules and polyatomic ions, the coordination number of an atom is calculated by simply counting the other atoms to which it is bonded either by single bonds or multiple bonds.
In the question we have asked the coordination number of oxygen in ${H_2}O(l)$, In ${H_2}O(l)$, the oxygen atom is bonded to two H atoms through covalent bond and there exists a hydrogen bonding between the ${H_2}O(l)$ molecules thus, is bonded to two other hydrogen atoms through $H - bonds$. Thus, there are four hydrogen atoms that are close to oxygen atoms, or in other words in contact with. Therefore, the coordination number of oxygen in ${H_2}O\;$ turns out to be $4$.

Additional Information: Water is an inorganic substance which is transparent in nature and is an odourless and colourless chemical substance, and when it comes to taste it is tasteless in nature. It is important to all forms of life, the one present on the land as well as water, and it does not consist of any calories nor any organic nutrients. Water is known to cover $71\%$ of the Earth’s surface, and mostly the seas and oceans. Small portions that are $1.7\%$ of the water is groundwater, and $1.7\%$ is present in the glaciers as well as ice caps of Antarctica and Greenland and is present in the air as vapours, and as clouds which are formed by the ice and liquid which is evaporated in the air.

Note:
A student should remember the fact that coordination number does not mean that it is the number of directly bonded atoms to an atom, whereas it refers to a contact/touch. In chemistry, crystallography, and materials science, the coordination number, also called ligancy, of a central atom in a molecule or crystal is the number of atoms, molecules or ions bonded to it.