The crystalline form of borax has

• Correct answer
  A

  Tetra nuclear ${\left[{\mathrm{B}}_4{\mathrm{O}}_5{\left(\mathrm{O}\mathrm{H}\right)}_4\right]}^{2-}$ unit
• B

  All boron atoms in the same plane
• Correct answer
  C

  Equal number of $\mathrm{s}{\mathrm{p}}^2$ and $\mathrm{s}{\mathrm{p}}^3$ hybridized boron atoms
• Correct answer
  D

  One terminal hydroxide per boron atom

Solution

(A) Having ${\left[{\mathrm{B}}_4{\mathrm{O}}_5{\left(\mathrm{O}\mathrm{H}\right)}_4\right]}^{2-}$ tetra nuclear (boron) unit.
(B) All boron atoms not in same plane.
(C) Two boron are $\mathrm{s}{\mathrm{p}}^2$ hybridised and two boron are $\mathrm{s}{\mathrm{p}}^3$ hybridised.
(D) One terminal hydroxide per boron atom is present.

Hence, the correct answer is options: 'A', 'C', 'D'.