The average number of inversions in an array of n records is n(n-1)/4. This is:

\Theta(n^2)
  • Better than \Theta(n^2)
  • Worse than \Theta(n^2)

n(n-1)/4 = n^2/4 - n/4.

From the rules on asymptotic analysis, \Theta(n^2/4 - n/4) is \Theta(n^2)