An electrically neutral atom consists of 15 neutrons,13 electrons, and a number of protons. what is its mass number

28

Explanation:

The atom is neutral, which means the quantity of electrons and protons square measure an equivalent. thus if there square measure 13 electrons, there square measure 13 protons. and therefore the nucleon number is neutrons and protons. thus 13+15 is 28

your answer would be a. 12.5 kg