Question

Which of the following isotopes of uranium is unstable?
A. U-234
B. U-235
C. U-238
D. All of the above

Answer 1

The isotopes of radioactive elements such as Uranium are unstable that means they are transformed into other elements by emitting or absorbing particles. If the given isotopes can be transformed then they are unstable.

Complete step by step answer: First one is U-234. U-234 is an indirect decay product of U-238. U-234 decays into Thorium-230 by alpha decay except for the tiny fraction of nuclei which undergoes spontaneous fission. Therefore, U-234 is an unstable isotope of Uranium.
Second one is U-235 is a much enriched isotope of Uranium which is used in operating nuclear reactors. The unstable nucleus of U-235 loses energy by emitting ions to reach a stable state. U-235 decays into Thorium -231 by alpha decay. Therefore, U-235 is also an unstable isotope of Uranium.
Third one is U-238. U-238 is the most common isotope of Uranium found in nature. Uranium-238 decays by alpha emission into Thorium-234, which itself decays by beta emission to Protactinium-234, which decays by beta emission to uranium-234, and so on and finally it stops at a stable isotope Lead-206.Therefore, U-238 is also an unstable isotope of Uranium.Therefore, the given options A, B and C are unstable. Option D is correct which states that all the given isotopes of Uranium are unstable.

Note: Isotopes of an element differ in the number of neutrons which means the isotopes of a given element have the same number of protons but different number of neutrons. Alpha decay is a radioactive decay in which a helium nucleus is emitted and beta decay is a radioactive decay in which an electron or a positron is emitted.