Which of the following species contain only $1$ electron?

The electronic configuration of a dipositive ion $M^{2+}$ is $2, 8, 14$ and its atomic mass is $56$. The number of neutrons in the nucleus would be :

List the isotopes of hydrogen,carbon,and chlorine,and specify the number of protons,electrons,and neutrons for each.

Which of the following are pairs of isotopes?

An isobar of ${ }_{20} Ca^{40}$ is

The atomic weight of an element is $39$. The number of neutrons in its nucleus is one more than the number of protons. The number of protons,neutrons,and electrons respectively in its atom would be