Odd Man Out

All except Cotton are synthetic fibres while cotton is a natural fibre.

In all other pairs, sum of the digits of both the numbers is the same.

All except Spider are flying insects.

In all other groups, the number of letters skipped between adjacent letters is uniform.

All except Blacksmith are tools

All except Cousin are relations of the same generation.

All except Eagle are scavengers.

In all other pairs, second number is 9 more than the first.

All except Minister are chessmen.

All other numbers expressed as a power of 2 minus one.Thus, 7 = 2³ – 1, 15 = 2⁴ – 1, 31= 2⁵ – 1