Which of the following best describes atoms? * a. Smallest basic units of matter
b. Single celled organisms
c. parts of a nucleus
Positively charged particles

a. Smallest basic units of matter

Atom: An atom is the smallest particles of a substance which may or may not exist in free state but takes part in chemical reactions.

Molecule: A molecule is a substance which exists in free state but doesn't take part in chemical reactions.

Laws of chemical combination:-

clouds form

solid ice forms on leaves.

water droplets form on grass.

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