Question

1 mole of diatomic element $X_2$ contains 34 and 40 moles of electron and neutron respectively. The isotopic formula of the element is

• A. $X_7{4}^{34}$
• B. $X_3{4}^{40}$
• C. $X_3{4}^{40}$
• D. $X_2{0}^{40}$

Answer 1

The correct option is B

$X_3{4}^{40}$

If one X2 molecule contains 34 electrons and 40 neutrons, then one atom of X has 17 electrons and 20 neutrons. Assuming that it is electrically neutral, it will also have 17 protons. The isotope has an atomic number of 17 (number of protons), and a mass number of 37 (number of protons + number of neutrons)

$X_{17}^{37}$