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Question:

The crystalline form of borax has:
Tetranuclear [B4O5(OH)4]²⁻ unit
All boron atoms in the same plane
Equal number of sp² and sp³ hybridized boron atoms
One terminal hydroxide per boron atom

Tetranuclear [B4O5(OH)4]²⁻ unit

All boron atoms in the same plane

One terminal hydroxide per boron atom

Equal number of sp² and sp³ hybridized boron atoms

Solution:

The correct options are
A. Tetranuclear [B4O5(OH)4]²⁻ unit
C. Equal number of sp² and sp³ hybridized boron atoms
D. One terminal hydroxide per boron atom

Correct formula of borax is Na₂[B₄O₅(OH)₄]·8H₂O. Borax has tetranuclear [B₄O₅(OH)₄]²⁻ unit. Only two B atoms lie in the same plane. Two Boron atoms are sp², two are sp³ hybridised. One terminal hydroxide is present per boron atom. Hence, options A, C, and D are correct.