Question

A thorium nucleus is formed, when a uranium nucleus emits an $\alpha$-particle. Atomic number of thorium is

• A. 92
• B. 90
• C. 40
• D. 94

Answer 1

Answer: (B)

Emission of $\alpha$-particle reduces the atomic number of the emitted by 2. Atomic number of thorium is 90 (atomic number of uranium is 92).