Question

Uranium ultimately decays into a stable isotope of:
A. Radium
B. Carbon
C. Lead
D. Neptunium

Answer 1

Hint: Lead is the last stable element among the heavier elements of the periodic table. Radioactive substance undergoes several modes of decay to make the radioactive nucleus stable. Uranium is a radioactive substance and produces lead on decay.

Complete Step by Step Solution:
All the actinides are radioactive. Actinides are highly unstable and undergo several modes of decay to stable the element. Here the element Uranium is an actinides. Thus Uranium is a radioactive element. It has an atomic number of $92$ . As Lead is the last stable element among the heavier elements of the periodic table thus all radioactive elements produce lead as the end product of decay. So, Uranium ultimately decays into a stable isotope of Lead.

Radium is a radioactive element so it cannot form as the ultimate decay product of Uranium.
Carbon is a main group element so it cannot form as the ultimate decay product of Uranium.
Neptunium is a radioactive element so, it cannot form as the ultimate decay product of Uranium.
Thus the correct option is C.

Additional information: Actinides are $5f$ block elements. They show different magnetic and spectral properties. The absorption band of actinides is weak due to orbitally forbidden $5f\to 5f$ transition. Again due to the crystal field effect they show a higher intense band than lanthanides. Actinides show several oxidation states up to $7$ . They can form complexes of higher coordination number like lanthanides.

Note: All the actinides are highly radioactive but the highest radioactivity is shown by uranium. These elements undergo decay to form stable nuclides and thus produce alpha particle or ray, beta particle and gamma ray.