Question

thallium-201 is a radioactive isotope used in the diagnosis of coronary artery disease. what is the mass number of the tl-201 isotope with the symbol \\(_{81}^{201}\text{tl}\\)? \\(\circ 13\\) \\(\circ 81\\) \\(\circ 204.4\\) \\(\circ 201\\) \\(\circ\\) none of the answers are correct.

Explanation:

Step1: Recall isotope notation

In the symbol for an isotope \(\ce{^{A}_{Z}X}\), \(A\) is the mass number, \(Z\) is the atomic number, and \(X\) is the element symbol.

Step2: Identify mass number in \(\ce{^{201}_{81}Tl}\)

For the isotope \(\ce{^{201}_{81}Tl}\), the superscript (top number) is the mass number. Here, the superscript is 201.

Answer:

201 (corresponding to the option with 201)