Uranium has atomic number 92. Its most common isotope is 238U, but the form used in nuclear bombs and nuclear power plants is 235U. How many neutrons are in each of these two isotopes of uranium

Atomic Number = Number of protons

Mass Number = Number of protons + Number of neutrons

Isotopes are simply atoms of an element with the same number of protons and different number of neutrons.

First Isotope - - 238U

Number of neutrons = Mass Number - Atomic Number

Number of neutrons = 238 - 92 = 146

Second Isotope - - 235U

Number of neutrons = Mass Number - Atomic Number

Number of neutrons = 235 - 92 = 143