Final answer:
Option (1), Nano is correctly defined as one billionth (10^-9) part of something, with the term 'nanometer' representing 1/1,000,000,000 meters in Physics and Chemistry, particularly in nanotechnology.
Step-by-step explanation:
The correct definition of "nano" is Option 1: One billionth (10^-9) part of something, such as a nanosecond. In scientific terms, particularly in Physics and Chemistry, a nano is a unit of measurement used to represent extremely small scales. When measuring distances, such as the diameter of atoms, we use nanometers (nm) where 1 nm equals 1/1,000,000,000 meters (10^-9 meters). This scale is significant in the field of nanotechnology, which deals with the development of products and components that lie between 1 and 100 nanometers.