Which of the following bonds will be the most ionic?

Elements $X$ and $Y$ have $2$ and $6$ electrons in their outermost shells,respectively. If they combine,what is the expected formula of the compound?

Among the following oxides,which has the maximum lattice energy?

The ionic bonds $X^{+}Y^{-}$ are formed when
$I$. electron affinity of $Y$ is high
$II$. ionization energy of $X$ is low
$III$. lattice energy of $XY$ is high
$IV$. lattice energy of $XY$ is low
Choose the correct code.

Sodium sulphate is soluble in water but barium sulphate is insoluble because:

Electrovalent bond formation depends on