Answer:
Sodium has a mass number of 23amu. Since sodium has 11 protons, the number of neutrons must be 23 – 11 = 12 neutrons.
Step-by-step explanation:
The mass number is given at the top left of the elements symbol, for example, sodium has a mass number of 23.
Sodium (Na) square from the periodic table. The mass number (23) is top-left. The atomic number (11) is bottom-left.
We know that the atomic number of sodium is 11. This tells us that sodium has 11 protons and because it is neutral it has 11 electrons.
The mass number of an element tells us the number of protons AND neutrons in an atom (the two particles that have a measurable mass).
Sodium has a mass number of 23amu. Since sodium has 11 protons, the number of neutrons must be 23 – 11 = 12 neutrons.