Answer: They have same number of protons but differ in number of neutrons.
Explanation:
Isotopes are defined as the species which have same number of neutrons but differ in the number of neutrons.
Uranium is the 92nd element of the periodic table.
Atomic number is defined as the number of protons that are present in an atom.
Atomic number = Number of protons
Mass number is defined as the sum of number of protons and neutrons that are present in an atom.
Mass number = Number of protons + Number of neutrons
For the given isotopes: [tex]_{92}^{239}\textrm{U},_{92}^{238}\textrm{U}\text{ and }_{92}^{235}\textrm{U}[/tex]
Number of protons = 92
Number of neutrons = 239 - 92 = 147
Number of protons = 92
Number of neutrons = 238 - 92 = 146
Number of protons = 92
Number of neutrons = 235 - 92 = 143
Hence, they have same number of protons but differ in number of neutrons.
