The atomic number represents the number of protons in an atom's nucleus. In an uncharged atom, the number of protons is always equal to the number of electrons. For example, carbon atoms include six protons and six electrons, so carbon's atomic number is 6.
There is 3 ways that an atom can be put together
The answer is: [D]: a reactant.
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That Answer would be...
C. Fireworks exploding
because this is a chemicals change the creates the fireworks.