Question

Which of the following is NOT an isotope of uranium?

• A. ${}_{92}^{236}\text{U}$
• B. ${}_{91}^{235}\text{U}$
  
• C. ${}_{92}^{239}\text{U}$
• D. ${}_{92}^{235}\text{U}$
• E. ${}_{92}^{238}\text{U}$

Answer 1

The correct option is B ${}_{91}^{235}\text{U}$

Isotopes of the same element have same atomic number but different mass number.

Atomic number of Uranium element is $92$.

Thus ${}_{91}^{235}U$ is not an isotope of uranium.