How many neutrons are present in 92U238?

A nucleus is represented as _ZX^A where Z is the number of protons (called atomic number), A is the sum of number of protons (Z) and number of neutrons (N) and is called mass number.

∴ Number of neutrons, N = A - Z

For example, ₉₂U²³⁸ has 92 protons, 238 - 92 = 146 neutrons and 238 nucleons (protons + neutrons).