Question

The radius of an oxygen atom is $0.73nm$ what does the symbol $nm$ represent?

Answer 1

Radius of an atom or we can say that the atomic radius of any chemical substance is nothing but what we call in day to day language measures the size of an atom . The $nm$ which is nothing but the nano meters or quantity with ten raised to power of nine. It is the measuring quantity basically which is generally measured in ten raised to the power of nine.

Complete step-by-step answer: Talking about the radius of an atom
Radius of an atom or we can say that the atomic radius of any chemical substance is nothing but what we call in day to day language measures the size of an atom. In proper language it is the typical distance from the centre of an atom to the outer shell. As we know that radius is of many types that may include ionic radius, covalent radius and many more. The different types of radius are due to the non defined boundaries of the outer shell.
Under most definitions the radii of the isolated neutral atoms range between several picometers .
Some radii are also in terms of the angstroms. When we talk about the visible light or the oxygen atom as mentioned above has the radius in terms of $nm$ which is nothing but the nano meters or quantity with ten raised to power of nine. It is the measuring quantity basically which is generally measured in ten raised to the power of nine.

Note: Measuring units are what we are discussing here . The$nm$ is the unit of measurement . These units help to measure the quantity and make the complex calculations easier.