Explanation:

• Term “nano” refers to the metric prefix 10-9. It means one billionth of something. “Nano” can be ascribed to any unit of measure. For example, you may report a very small mass in nanograms or the amount of liquid in one cell in terms of size.
• Nanoscience is the study of structures and materials on the scale of nanometers. To give you an idea of how long a nanometer is, this printed page is about 75,000 nanometers thick. When structures are made small enough—in the nanometer size range—they can take on interesting and useful properties. It can study with the help of Quantum mechanics.

Hence option 1st is correct.