Find the odd man out? 28, 12, 4, 2, -2

Here the given series 28, 12, 4, 2, -2 follows a pattern that

$28 28 - 24 = 28 - 16 = 1212 - 23 = 12 - 8 = 44 - 22 = 4 - 4 = 0 (\mathrm{NOT} 2)0 - 21 = 0 - 2 = -2$

Hence, the odd man in the given series is 2.