The phosphide ion has an electronic structure similar to that of:

Which of the following elements is isoelectronic with $Na^{+}$?

In the two elements, ${ }_{Z_1} A^{M_1}$ and ${ }_{Z_2} B^{M_2}$, the following relations are true. $M_1 \neq M_2$ and $Z_1 \neq Z_2$ but $M_1-Z_1=M_2-Z_2$. These elements are ($M$ is atomic weight, $Z$ is atomic number)

Consider an imaginary ion ${}_{22}^{48}X^{3-}$. The nucleus contains '$a$'$\%$ more neutrons than the number of electrons in the ion. The value of '$a$' is $.....$ [nearest integer].

If a neutral atom has $2, 8,$ and $5$ electrons in $K, L,$ and $M$ shells respectively,what is its atomic number?

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