An element has an electronic configuration of $2, 8, 18, 1$. If its atomic weight is $63$,then how many neutrons will be present in its nucleus?

Isotopes of an element have

Which of the following is correct?

What is the atomic number and the number of electrons in a hydrogen atom (containing $1$ proton) and a sodium atom (containing $11$ protons) respectively?

$_{20}X^{40}$ and $_{21}X^{40}$ are

The mass numbers of two elements $X$ and $Z$ are $52$ and $75$ respectively. $X$ contains $16.6 \%$ more neutrons compared to protons. $Z$ contains $27.3 \%$ more neutrons compared to protons. $X$ and $Z$ are respectively