Static assignment is used to ensure a particular device always receives the same IP address from a DHCP server. This can be achieved by reserving a specific IP address in the DHCP server configuration and associating it with the device's MAC address, thereby ensuring the device receives the same IP address even after rebooting or rejoining the network. Dynamic assignment, on the other hand, is incorrect because it allows the DHCP server to assign IP addresses to devices randomly from a pool of available addresses. Exclusion ranges and scope options are used to define which addresses are not to be given out and to configure additional settings for the DHCP scope, respectively, and are not related to assigning a static IP address to a device.