An isotope,X,of a particular element has an atomic number of 15 and a mass number of 31.Therefore:

Question

Quizplus · Accepted Answer

A) The atomic number of 15 matches the atomic number of phosphorus, so X is an isotope of phosphorus. 
B) The mass number of 31 minus the atomic number of 15 gives a neutron number of 16. 
C) The atomic mass of X can be calculated as 31 u, which is close to the atomic weight of phosphorus (30.97 u), but not exactly the same due to the presence of isotopes with different masses.

An Isotope,X,of a Particular Element Has an Atomic Number of 15