This question has 4 part(s).

Sodium chloride and iodine are both solids. Sodium chloride does not melt until it reaches a temperature of 1074 K yet iodine sublimes when heated gently, giving off purple vapours. Sodium chloride will conduct electricity when molten and iodine is a very poor conductor of electricity.

i) State the type of crystal structure for each of iodine and sodium chloride.

ii) Explain why iodine vaporises easily.

iii) Explain the differences in electrical conductivity of sodium chloride and iodine.

Calcium will react with the elements of Group 7 to form ionic compounds, which have an ionic lattice structure.

Describe what is meant by the term ionic lattice.

An ionic compound has the empirical formula H₄N₂O₃. 

Suggest the formulae of the ions present in this compound.