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 graph of the function y = f(x) is symmetrical about the line x = 2, then

The range of the function f(x) = $${}^{7 - x}{P_{x - 3}}$$ is