Find the odd number / letters / word from the given alternative:

Troop
Group
Mob
Class

The odd word from the given alternatives is mob.

A troop is a small group of soldiers or scouts. A group is a number of people or things that are together or are considered to be together. A class is a group of people who are taught together or who have the same job or interest. A mob is a large, disorderly crowd of people, especially one that is intent on violence.

The word “mob” is the odd word out because it is the only word that is associated with violence. The other words are all associated with groups of people who are not necessarily violent.