Answers:

(i)

Domain of f = R (set of real numbers)

Square of a real number is always positive or zero.

∴ range of f = R⁺∪ {0}

(ii)

f(x) = 4

x² = 4

x² – 4 = 0

(x – 2)(x + 2) = 0

∴ x = ± 2

∴ {x: f(x) = 4} = {–2, 2}