Substracting the atomic number of an atom from its mass number results
in the number of
a. neutrons
b. protons
c. electrons
d  energy levels

Dear neener:

Thank you for your question. 

The atomic number is the number of protons in the atom.

The mass number is the number of protons in the atom, plus the number of neutrons.

This should be enough information to answer your question. 


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I hope this helps!


Best Regards,
blader-ga