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Boric acid has a polymeric layer structure in which planar $B{{O}_{3}}$ units are joined by:
(A)- covalent bonds
(B)- two centre-two electron bonds
(C)- coordinate bonds
(D)- hydrogen bonds

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Last updated date: 13th Jun 2024
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Answer
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Hint: Boric acid (${{H}_{3}}B{{O}_{3}}$) in solid crystalline state has two dimensional layered structure. Hydrogen bond is a weak bond between an electronegative atom like N, O, F and a hydrogen atom bonded to another electronegative atom.

Complete answer:
To understand the structure of boric acid (${{H}_{3}}B{{O}_{3}}$), consider the ground state electronic configuration of boron.
B (in ground state): $1{{s}^{2}}2{{s}^{2}}2{{p}^{1}}$
One electron from 2s moves to 2p-orbital in the excited state and the electronic configuration becomes: $1{{s}^{2}}2{{s}^{1}}2{{p}^{2}}$
One s and two p-orbitals are now available to bond with three oxygen atoms. Therefore, the hybridization of the central atom B is$s{{p}^{2}}$.
Now, since only one electron of each oxygen atom is used in the bond formation. The borate ion formed is a trivalent ion,$BO_{3}^{-3}$. Due to $s{{p}^{2}}$ the geometry of $BO_{3}^{-3}$ is trigonal planar. In the triangular $BO_{3}^{-3}$, three oxygen atoms are present at the corners of an equilateral triangle.

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Boron is attached to three oxygen atoms and each oxygen is bonded to one hydrogen. Each such unit is ${{H}_{3}}B{{O}_{3}}$. These units are bonded together through hydrogen bonds to give a two-dimensional layered structure of boric acid.
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So, the correct answer is “Option D”.


Additional Information: Boric acid or orthoboric acid is a weak monobasic acid. It does not donate protons but accepts a pair of electrons ${{H}_{3}}B{{O}_{3}}$ from and thus behaves as a Lewis acid. It has a soapy touch and is moderately soluble in water.

Note: Bonds between boron and oxygen atoms are covalent. One ${{H}_{3}}B{{O}_{3}}$ unit is joined to another through hydrogen bonding between oxygen of one ${{H}_{3}}B{{O}_{3}}$ to the hydrogen of another ${{H}_{3}}B{{O}_{3}}$.