Answer:
D. neptunium
Explanation:
Neptunium was the first transuranium element discovered in lab. All transuranium elements have atomic number greater than 92. The atomic number of Uranium is 92. Neptunium has atomic number 93 and mass number 237. Neptunium has 7 valence electrons, 93 electrons and 93 protons. It is highly radioactive and unstable.
