Discovery Range Sets in ServiceNow Discovery offer a flexible way to manage and identify networks. They simplify the administration of network discovery by allowing administrators to define groups of IP ranges.
This organization helps in effectively managing and targeting different network segments without needing to define each IP range in individual Discovery Schedules. Range Sets do not necessarily show the number of IPs in a subnet, nor are they the only way to define multiple IP ranges in a schedule.

The Credential Affinity table is a table that associates an IP address and a credential in Discovery1. It is used to store the credential that was successfully used to access a device during Discovery2. It can also be used to manually assign a credential to an IP address or a range of IP addresses3. The other options are not tables that associate an IP address and a credential in Discovery. The Service Affinity table is a table that associates a business service and a credential. The Service CI Association table is a table that associates a business service and a configuration item (CI). The Tags table is a table that stores tags that can be applied to records in any table.
References: 1: Credential Affinity table 2: Credential affinity 3: Manually assign a credential to an IP address :
Service Affinity table : Service CI Association table : Tags table

Credential affinity is an association between a set of credentials and a device on your network. When Discovery or Orchestration first attempts to access a device, they try all available credentials until a valid one is found. Once a valid credential is found, it is recorded in the dscy_credentials_affinity table, and further discovery processes rely on this information. If the credentials are modified or changed, the process will be repeated until a valid credential is found and updated in the same table. Credential affinity allows Discovery to use the most efficient and successful credential for each device, and avoid unnecessary credential failures.
References: Credential affinity for Discovery and Orchestration, Credential Management in ServiceNow discovery