What is the difference between ${\text{CO}}$ and ${\text{Co}}$?

Hint: Molecular representation itself has no small letter. A molecular representation can have a small letter if the atom present in that molecule has a small letter in its symbol. To answer this question we should have the basic knowledge of representation of atoms and the molecules.

Complete Step by step answer: A single capital letter that is the initial letter of the atomic name is used to represent the atom.
An atomic representation can have two letters if the first letter already represents some other atom. In that case the second letter will be a small letter.
So, a capital letter or a capital with a small letter represents the atom and is known as an atomic symbol.
The molecule representation has a capital letter if the atoms present in that molecule are represented by only capital letters.
The molecule representation can have small letters if the atom present in that molecule is /are represented by capital letter plus small letter.
The C in ${\text{CO}}$ represent the carbon atom and the O represent the oxygen atom. So, the${\text{CO}}$ is a molecule made up of carbon and oxygen atoms.
Whereas the ${\text{Co}}$ represents an element named as Cobalt.
One can think C in ${\text{Co}}$ represents the carbon atom and ${\text{Co}}$ is a molecule but in that case, the small letter ’o’ does not represent any atom so, the whole ${\text{Co}}$ represents an atom Cobalt. Because the C symbol is used for carbon, to avoid the confusion ${\text{Co}}$ is used as a symbol of Cobalt.
Therefore, ${\text{CO}}$ is a molecule whereas the ${\text{Co}}$ is an atom.

Note: The molecule representation includes the letter that represents the atomic symbol of the atoms present in that molecule. An atomic symbol can have a single capital letter but cannot have a single small letter.