The number set {1/2, 1/4, 1/8, 1/16, 1/32} consists of fractions that can be expressed as ratios of two integers, where the denominators are not equal to zero.
The best matching category for the given set is:
3). Rational Ratios with a denominator ≠ 1
These numbers are rational numbers, and since they all have a denominator other than 1, they fit into this specific category.