Identify the incorrect statement:

Let's analyze each option step by step to identify the incorrect statement.

Starting with option A: In the ion $$(Si_3O_9)^{6-}$$, the tetrahedral SiO$$_4$$ units share two oxygen atoms. Silicate ions are composed of SiO$$_4$$ tetrahedra that can share corners. In a cyclic trimer like $$(Si_3O_9)^{6-}$$, each silicon atom is bonded to four oxygen atoms. Two of these oxygen atoms are shared with adjacent silicon atoms (bridging oxygens), and the other two are terminal. Therefore, each SiO$$_4$$ unit indeed shares two oxygen atoms, making this statement correct.

Now option B: Trialkylchlorosilane on hydrolysis gives R$$_3$$SiOH. Trialkylchlorosilane has the formula R$$_3$$SiCl. When hydrolyzed, the reaction is R$$_3$$SiCl + H$$_2$$O → R$$_3$$SiOH + HCl. However, R$$_3$$SiOH (trialkylsilanol) is unstable and undergoes condensation with another molecule of R$$_3$$SiOH to form a disiloxane: 2 R$$_3$$SiOH → R$$_3$$SiOSiR$$_3$$ + H$$_2$$O. Thus, the final stable product of hydrolysis is R$$_3$$SiOSiR$$_3$$ (disiloxane), not R$$_3$$SiOH. Therefore, the statement that hydrolysis gives R$$_3$$SiOH is incorrect because the silanol is an intermediate that dehydrates.

Option C: SiCl$$_4$$ undergoes hydrolysis to give H$$_4$$SiO$$_4$$. Silicon tetrachloride (SiCl$$_4$$) reacts vigorously with water: SiCl$$_4$$ + 4 H$$_2$$O → Si(OH)$$_4$$ + 4 HCl. Si(OH)$$_4$$ is orthosilicic acid, commonly written as H$$_4$$SiO$$_4$$. Although H$$_4$$SiO$$_4$$ may dehydrate further to silica gel, it is the initial and direct product of hydrolysis. Thus, this statement is correct.

Option D: $$(Si_3O_9)^{6-}$$ has a cyclic structure. This ion is known as cyclotrisilicate, where three SiO$$_4$$ tetrahedra are linked in a ring by sharing oxygen atoms. Each silicon atom forms part of a three-membered ring, confirming a cyclic structure. Hence, this statement is correct.

After evaluating all options, only option B is incorrect because trialkylchlorosilane hydrolysis yields disiloxane (R$$_3$$SiOSiR$$_3$$), not R$$_3$$SiOH.

Hence, the correct answer is Option B.