$($a$)$ What two factors affect the lattice energy of a substance?

$($b$)$ Would you expect NaI to have a lower or higher lattice energy compared to NaCl $?$ Explain

$($c$)$ Which compound should have the higher enthalpy of solution $(H_{\text{s}\text{o}\text{l}})?$ Explain

$($d$)$ If the lattice energy and the enthalpy of hydration for NaI is $-686k\frac{J}{m}ol$ and $-694k\frac{J}{m}ol,$ respectively, calculate the enthalpy of solution for NaI.

$($e$)$ Calculate the enthalpy of solution for NaCl, if the lattice energy is $-779k\frac{J}{m}ol$ and the enthalpy of hydration for NaCl is $-774k\frac{J}{m}ol.$

$($f$)$ Can the solutions in $($d$)$ and $($f$)$ form? Explain.