From the given choices select the odd man out

In a numeric “odd one out” set built from prime factorisation, the values usually share a common structural feature — such as having several distinct prime factors — while exactly one value is built differently, most often as a single prime raised to a power. The way to solve it: find the prime factorisation of each number and compare how many DISTINCT primes each one uses.

1. 10 = 2 × 5 → 2 distinct prime factors.

2. 30 = 2 × 3 × 5 → 3 distinct prime factors.

3. 68 = 22 × 17 → 2 distinct prime factors.

4. 128 = 27 → only 1 distinct prime factor.

Three of the four values (10, 30, 68) are each built from two or more distinct primes; only 128 is built from a single prime (2) raised to a power, so 128 does not share the group's structure.

Cross-check: 128 is also the only value with no odd factor greater than 1 (every factor of 27 is itself a power of 2, so 1 is the sole odd one), and the only value that is not a two-digit number — both independent observations point to the same option.

Hence, 128 is the odd man out.