Question

One species of element $X$ has an atomic number of $9$ and a mass number of $19$; one species of element $Y$ has an atomic number of $10$ and a mass number of $19$. Which of the following statements about these two species is true?

• A. They are isotopes
• B. They are isomers
• C. They are isoelectronic
• D. They contain the same number of neutrons in their atoms
• E. They contain the same total number of protons plus neutrons in their atoms

Answer 1

The correct option is E They contain the same total number of protons plus neutrons in their atoms

we know that number of protons is atomic number.

and net charge on an atom is given by number of protons minus number of electrons.

Mass number = number of neutrons +number of protons.