The correct answer is C. 92.
Transuranium elements are the chemical elements with atomic numbers greater than 92, the atomic number of uranium. They are all synthetic elements, meaning that they have not been found in nature. The first transuranium element, neptunium, was discovered in 1940. As of 2023, 118 elements have been discovered, of which 94 are transuranium elements.
Transuranium elements are all radioactive, meaning that they decay into other elements over time. The half-lives of transuranium elements vary widely, from a few milliseconds to billions of years. The longest-lived transuranium element is plutonium-244, with a half-life of 80 million years.
Transuranium elements are not found in nature because they are too unstable. They are only produced artificially in nuclear reactors or particle accelerators. Transuranium elements have a variety of uses, including in nuclear weapons, nuclear power plants, and medical research.
Option A is incorrect because the atomic number of uranium is 92. Option B is incorrect because the atomic number of actinium is 89. Option D is incorrect because the atomic number of curium is 96.