calculate the potential energy per ion for an infinite one dimensional crystal which will alternate sodium and chloride ions

Explanation:

given data

we will take here

sodium ions = positive charge

chloride ions = negative cgarge

solution

as when we take Na positive charge so Number of origin is

d = 0

and here pair of ions with negative charge at d = - r

and d = +r

therefore

we will use here Taylor series approx method

and N/2 pair will contribute here

so

so energy per ion will be here

i believe the answer is a.

b.final