Given the subscription’s resources (as shown), which proximity placement group should be assigned to VMSS1?

Proximity placement groups are designed to bring Azure resources, like virtual machines, physically closer together to reduce network latency. For a Virtual Machine Scale Set (VMSS), all instances within that scale set must belong to the same proximity placement group. In this scenario, VMSS1 is already associated with Proximity1. Therefore, any new or existing instances of VMSS1 must also be assigned to Proximity1 to maintain the low-latency grouping. Assigning VMSS1 to Proximity2 or Proximity3, or a combination including them, would either violate the single-group rule for a VMSS or move the VMSS to a different proximity group, which is not the intent when an existing association is present.