Which of the following commands is used to deactivate a network interface?

The `ifdown` command is a standard utility on Linux systems, typically used within network configuration scripts, to deactivate a specified network interface. It handles the process of bringing down the interface, releasing its IP address, and stopping associated network services.

`ipdown` is not a standard or recognized command for deactivating network interfaces in Linux; the correct utilities are `ifdown` or `ip link set dev <interface> down`.

`net` is a general command with various network-related subcommands but does not directly deactivate an interface by itself.

`netdown` is not a standard command used in Linux to deactivate a network interface.