What is the number of neutrons in #""_(5)^(10) "B"#?
This atom has 5 neutrons.
The bottom number (5) is the atomic number. The atomic number tells you how many protons an atom has.
The top number is the mass number (10). The mass number tells you the mass of the atom. The mass of the atom is the combined number of protons and neutrons. Electrons don't contribute much mass at all, so we ignore them for questions like this.
To find the number of neutrons, just take the mass and subtract the number of protons.
10 - 5 = 5
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