Question

What is an atom and moleule ? What is the order of magnitude of mass of one atom ? What are isotopes?​

Answer 1

Atom is a fundamental piece of matter. Atoms are very small, they are smaller than anything that we can imagine.

Molecule is the smallest particle of an element or a compound capable of independent existence under ordinary conditions.

The gram (10−3 kg) is an SI derived unit of mass. However, the names of all SI mass units are based on gram, rather than on kilogram; thus 103 kg is a megagram (106 g), not a "kilokilogram". The tonne (t) is a SI-compatible unit of mass equal to a megagram, or 103 k

Isotopes are defined as atom of same element, which have different mass numbers.