$a > b > 0$. Which of these is always true?

Explanation

1. 01

   For positive numbers, taking reciprocals reverses the order: the larger number has the smaller reciprocal.

2. 02

   So $\frac{1}{a} < \frac{1}{b}$. The others reverse true facts: $a^{2} > b^{2}$, $-a < -b$, $a - b > 0$.