How to find the number of neutrons in manganese?

One way to find the neutrons in the atom of a given element is by using its atomic number and atomic mass. The atomic number of an element is the number of protons it has, while the atomic mass is a measure of both the number of protons and number of neutrons.

In other words,

atomic number = number of protons

atomic mass = number of protons + number of neutrons

Thus, the number of neutrons can be determined by subtracting the atomic number from the atomic mass. That is,

Number of neutrons = atomic mass - atomic number

The atomic number of manganese is 25 and its atomic mass is 54.94 (~ 55). Thus, the number of neutrons in a manganese atom are 30 (= 55-25).

Please note that a number of elements have isotopes, atoms with different atomic mass (but same atomic number). In that case, the atomic mass and atomic number can be similarly used to determine the number of neutrons.

Hope this helps.