Explanation:

- Option 1: Jealousy

- Jealousy is an emotional response to the perception of threat or competition. It can influence individual behavior but isn’t central to reference group behavior.

- Option 2: Relative Deprivation

- Relative deprivation is the feeling of discontent when comparing one’s situation with others. It is a key driver in reference group behavior as individuals assess their status and circumstances relative to others.

- Option 3: Out-group

- Out-group refers to groups to which a person feels they do not belong. While important in social dynamics, it is not the primary factory in reference group behavior.

- Option 4: Membership

- Membership signifies belonging to a group. It affects behavior but isn’t the primary lens of reference group behavior, which relies more on comparison.