An element has an atomic mass of $19$ and an atomic number of $9$. How can its ion be represented?

The number of protons,neutrons,and electrons in the element $_{89}X^{231}$ are respectively:

Which of the following sets of ions represents a group of isoelectronic ions?

Assertion : The sum of protons and neutrons is always different in isobars.
Reason : Isobars are atoms of different elements having same mass number but different atomic number.

$({}_{32}Ge^{76}, {}_{34}Se^{76})$ and $({}_{14}Si^{30}, {}_{16}S^{32})$ are examples of

The pair,in which ions are isoelectronic with $Al^{3+}$ is ..... .