this is a repeated question,
still I'll just summarize the concept:
when we say f(n) = O(g(n)), we mean f(n) <= c.g(n) alright ?
and when we say f(n) = Ω (g(n)), then we mean f(n) >=g(n)
So when we say g(n) = max( Ω (n),O(n)), then it can be understood as g(n) <= n or g(n)>=n
clearly g(n) >=n is greater of the two is comes in Ω ! that's why answer is Ω (n).