The symbol for a radioactive nuclide is 56131Ba Which statement is correct?

In nuclide notation, the upper number is the mass number and the lower number is the atomic number. For ¹³¹₅₆Ba, the mass number is 131, so the correct statement is that the nuclide’s mass number is 131. It has 56 protons and 131 − 56 = 75 neutrons.

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