Question

Name the quantity(s) which is (are) measured in the $nm$.
A. Length
B. Density
C. Volume
D. Mass

Answer 1

$nm$ stands for nanometers. This word was influenced by the Greek language in earlier centuries. It is a unit formed to measure microscopic dimensions. Nowadays with the material of these sizes, many innovations are made for humankind.

Complete answer:
In this word or innovation and research, people have to go through a lot of complex and précised calculations and practical performances. In the microscopic world, it is hard to measure the dimension of matter in the slandered form. Can you measure the radius of an electron in meters/ cm/mm or so?
Yes, we can measure that but what would be a complex number with which it will be really hard to do any calculation work. So for the ease of the students and the researchers a new subunit was introduced in the field of science which was termed as nanometer.
A nanometer is an American spelling that is used as a unit of length in the metric system.
One nanometer is given as $0.000000001m$. In scientific notation, it can be also written as, $1nm = 1\times {{10}^{-9}}m$ .
In engineering terms, it is simply written as $\dfrac{1}{1\,000\,000\,000}meters$ .
Nanometers are often used to measure microscopic dimensions such as the diameter of atoms. For example, the diameter is about $0.06nm$. It is used in many research-oriented calculations such as distance in the DNA strands, the radius of electrons, etc.

Thus, the correct option to satisfy the question is Option A.

Note:
Nanometers was earlier known as the millimicrometre or millimicron. This was often denoted by the symbol $m\mu$. Then afterward the name combines the SI prefix Nano (ancient Greek word refers to ‘dwarf’) with the present unit name meter (from Greek ‘unit of measurement’).