Which of the following reactions is associated with the lattice energy of $Cs_2O$ ($\Delta H_{latt}$)?
$2Cs^+(aq) + O^{2-}(aq) \rightarrow Cs_2O(s)$
$2Cs^+(g) + O^{2-}(g) \rightarrow Cs_2O(s)$
$2Cs(s) + \frac{1}{2}O_2(g) \rightarrow Cs_2O(s)$
$Cs_2O(s) \rightarrow 2Cs^+(aq) + O^{2-}(aq)$
$Cs_2O(s) \rightarrow 2Cs^+(g) + O^{2-}(g)$