Aneutral atom possesses an atomic number of 15 and an atomic mass of 31. three electrons are gained. what is the result of this conversion?

On a neutral state, the number of proton of a substance will be equal to the number of its electron (in this case, it has 15 electrons)
When three electrons are gained, the total number of electron will change to 18, this result in the substance became a negatively charged ion of 3-

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