The element which forms a basic oxide has the atomic number of:

The atomic numbers of three elements $\mathrm{X}, \mathrm{Y}$ and $\mathrm{Z}$ are $2, 6$ and $10$ respectively.

Which two elements belong to same group?

The atomic numbers of three elements $\mathrm{X}, \mathrm{Y}$ and $\mathrm{Z}$ are $2, 6$ and $10$ respectively.

Which two elements belong to same period?

An atom has the electron structure $2, 7$.

What is the atomic number of this atom?

An atom has the electron structure $2, 7$. To which of the following the atom would be similar and why?

${}_7{}^{}\mathrm{N}, {}_{15}{}^{}\mathrm{P}, {}_{17}{}^{}\mathrm{Cl}, {}_{18}{}^{}\mathrm{Ar}$

Consider the following elements: ${}_{20}{}^{}\mathrm{Ca}, {}_8{}^{}\mathrm{O}, {}_{18}{}^{}\mathrm{Ar}, {}_{16}{}^{}\mathrm{S}, {}_4{}^{}\mathrm{Be}, {}_2{}^{}\mathrm{He}$

Which of the above elements would you expect to be very stable?