Final answer:
The most unstable group according to Georg Simmel is a dyad, because if one member leaves, the group ceases to exist, unlike a triad, which can survive the loss of one member.
Step-by-step explanation:
According to Georg Simmel, the most unstable group is a dyad, or a two-member group. This is because in a dyadic relationship, if one person withdraws, the group can no longer exist. For instance, in the case of a divorce, when one partner leaves, the marital group ceases to exist, or if two best friends stop communicating, their dyadic group ends.
On the other hand, a triad which is a three-member group, can sustain the withdrawal of one member, leaving the other two to continue the group's existence. Additionally, in a triad, different dynamics such as majority opinion can develop, which is not possible within a dyadic relationship.