Question

Given,${U^{235}}$ and ${U^{238}}$ are separated by
A.Sublimation
B.Gaseous diffusion
C.Electrolysis
D.Precipitation

Answer 1

An isotope is one of two or more forms of the same chemical element. Isotopes of the same element have identical chemical properties, they cannot be separated by chemical methods. The only thing that makes them different is their different masses due to the different numbers of neutrons. Isotope separation is a process of element enrichment by the physical separation of isotopes in a substance. Sublimation, Electrolysis and Precipitation are all chemical reactions.

Complete answer:
Different isotopes of an element have the same number of protons in the nucleus, giving them the same atomic number, but a different number of neutrons giving each elemental isotope a different atomic weight.
Given ${U^{235}}$ and ${U^{238}}$ are two isotopes of the uranium.
Since these are two isotopes of the same element, there will not be any chemical difference between them.
Gaseous diffusion is a uranium enrichment process used to prepare uranium for use in fabricating fuel for nuclear reactors by separating its isotopes based on their slight difference in velocity. Lighter isotopes diffuse faster through a porous membrane or vessel than do heavier isotopes.
Hence the correct Option is 2) Gaseous diffusion.

Note:
Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. Electrolysis is a process by which electric current is passed through a substance to effect a chemical change. The process is carried out in an electrolytic cell. Precipitation is a technique used to separate a mixture based on the solubility of its components. The solubility of a compound depends on the ionic strength of the solution, its pH, and temperature.