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

• A
  $A$ is true, $R$ is true and $R$ is the correct explanation for $A$
• B
  $A$ is true, $R$ is true but $R$ is not the correct explanation for $A$
• C
  $A$ is true but $R$ is false
• D
  $A$ is false but $R$ is true