Why sodium aluminate is considered as a complex salt even though there is no third bracket used?

Dear student,
A complex compound is a compound formed from a lewis acid and a lewis base. They do not dissociate into its constituent ions in solutions

   eg: 1.  Fe(CN)₂ + 4KCN ---> K₄[Fe(CN)₆]

          K₄[Fe(CN)₆] on dissociation gives 4K⁺ + [Fe(CN)₆]^4- 

In K₄[Fe(CN)₆] the individual components lose their identity. The metal of the complex ion is not free in solution unlike the metal in double salt solution.

2.NaAl(OH)4 is a complex salt,
 $$\begin{gathered} It is a complex salt,and it dissociates into N{a}^{+} and {\left[Al{\left(OH\right)}_4\right]}^{-}. \\ The metal of the ion complex is not free in solution hence it is a complex salt \end{gathered}$$
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