We define reactions uniquely depending on the reactants and products. Here are examples related to your question.
Formation: Na(s) + (1/2)Cl$_2$(g) $\rightarrow$ NaCl(s)
Lattice Formation: Na$^+$(g) + Cl$^-$(g) $\rightarrow$ NaCl(s)
Solution: NaCl(s) $\rightarrow$ NaCl(aq)
Hydration: Na$^+$(g) $\rightarrow$ Na$^+$(aq)
Atomization: Na(s) $\rightarrow$ Na(g)
A significant observation here is that the STATE of the reactants and products is also required because it is a unique identifier.
As to your questions ...
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We can convert NaCl(s) to gaseous ions experimentally through processes that may involve multiple steps, including vaporization and ionization.
- During the dissolution of NaCl(s), why is there no formation of solid ions first but directly, it states that gaseous ions of NaCl are formed?
The experimental dissolution of NaCl(s) does not involve formation of gaseous ions. It involves formation and solvation of aqueous ions. The two steps (dissolution and solvation) are often not easily separated.
What you refer to is the case where we imagine the dissolution of NaCl(s) happening through a set of steps that include the formation of gaseous ions. The process to combine reaction steps that go from a given set of reactants to a given set of products is formalized in what is called a Born-Haber cycle. This example demonstrates how some of the above reactions fit into a Born-Haber cycle diagram for NaCl(s).
Just because we imagine a reaction path on the Born-Haber cycle does not mean that the reaction occurs experimentally. Indeed, one power to the Born-Haber cycle is to back-calculate an energy for a reaction that does not occur experimentally but that has significant theoretical utility as a building block to obtain other values.