Correct option: (ii) The lower bound (as the intended distinction in this question).

Big-Ω (Omega) notation describes an asymptotic lower bound on a function's growth. Formally, (f(n) \in \Omega(g(n))) if there are constants (c>0) and (n_0) such that (f(n) \ge c,g(n)) for every (n \ge n_0).

Important clarification: Big-Ω does not inherently mean best-case complexity. Upper bound, lower bound and tight bound are properties of asymptotic notation; best-case, worst-case and average-case describe which case of an algorithm's input behaviour is being analysed. A lower bound can be applied to any of those functions.

• Big-O: asymptotic upper bound.
• Big-Ω: asymptotic lower bound.
• Big-Θ: asymptotically tight bound.

Therefore, choose option (ii) for the lower-bound part, but do not memorize “Ω = best case” as a general rule.