What is the significance of ionisation enthalpy?

Explain the following.

Electronegativity of $\mathrm{B}\mathrm{r}$ is greater than $\mathrm{}\mathrm{S}\mathrm{e}$.

Five elements $\mathrm{A},\mathrm{B},\mathrm{C},\mathrm{D}$ and $\mathrm{E}$ have atomic number $1,2,5,6$ and $8$ respectively. Answer the following questions.
(i) Which element forms positive ions?

(ii) Which element has five electrons in the valence shell?

(iii) Which element has the highest electron affinity?

(iv) Which element has the highest ionisation potential?

Properties of the elements are given below.

Where would you locate the following element in the periodic table?

An element with variable (more than one) valency stored under water.