Which of the following shows dimerisation?

Which of the following statements is correct regarding boron hydrides?

Aluminium $(III)$ chloride forms a dimer because aluminium

Which of the following statements is correct?

The number of acidic protons in $H_{3}PO_{3}$ is:

Assertion $(A)$: $[B(OH_2)_6]^{3+}$ and $[B(OH)_4]^{-}$ form octahedral and tetrahedral structures.
Reason $(R)$: Being electron deficient, boron readily reacts with Lewis bases like $H_2O$ and $OH^{-}$.
The correct option among the following is