The most likely cause of the internet issue is B. The DHCP scope is full.

A DHCP scope is a range of IP addresses that a DHCP server can assign to DHCP clients on a network. A DHCP scope has a start address and an end address, and it can also have some excluded addresses that are not available for lease. A DHCP scope can have various options, such as subnet mask, default gateway, DNS server, etc., that are applied to the DHCP clients along with the IP address. A DHCP scope also has a lease time, which is the duration that a DHCP client can use an IP address before renewing it or releasing it. A DHCP scope can have reservations, which are fixed IP addresses that are assignedto specific DHCP clients based on their MAC addresses12

If a DHCP scope is full, it means that there are no more IP addresses available for lease in the scope. This can happen if the number of DHCP clients exceeds the number of IP addresses in the scope, or if the lease time is too long and the IP addresses are not released or reused frequently enough. If a DHCP scope is full, any new or existing DHCP clients that request an IP address from the DHCP server will not receive one, and they will not be able to access the network or the internet12

In this scenario, users are able to connect to the wireless network, but they are unable to access the internet. The network administrator verifies connectivity to all network devices, and there are no ISP outages. The server administrator removes the old address leases from the active leases pool, which allows users to access the internet. This indicates that the DHCP scope is full, and that removing the old leases frees up some IP addresses for lease in the scope. Therefore, option B is the most likely cause of the internet issue.