When atoms are joined together, they form A. protons
B. electrons
C. molecules
D. nuclei

hi

Explanation:

protons,electrons and neutrons form atoms and

atoms form molecules

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molecules

Explanation:

When atoms are joined together, they form molecules.

The nuclei is the centre part of an atom which contains proto s in it and electrons are the negatively charged sub-atomic particles which is present outside the nuclei. These are located inside the atoms but molecules are the smallest particle of an element or compound. They are formed my combining atoms together.