The states of hybridization of boron and oxygen atoms in boric acid (H₃BO₃) are respectively

Which one of the following has the regular tetrahedral structure?
(Atomic nos : B = 5, S = 16, Ni = 28, Xe = 54)

The maximum number of 90° angles between bond pair of electrons is observed in

The domain of the function
$$f\left( x \right) = {{{{\sin }^{ - 1}}\left( {x - 3} \right)} \over {\sqrt {9 - {x^2}} }}$$