Which command will add the execute permission for everyone to a file named file5?

The command to add execute permission for everyone to a file named file5 is indeed "chmod a+x file5". In the context of the chmod command, the 'a' in 'a+x' stands for "all", which includes the user (owner), group, and others. The '+x' indicates that execute permission is being added.

When you use this command, it modifies the file permissions so that all users (regardless of their ownership or group affiliation) can execute the file. This is particularly important for scripts or executables that need to be run by multiple users in a system.

The other commands provided do not achieve this objective. One command removes read, write, and execute permissions from the user, which would be counterproductive. Another command attempts to add different permissions for user, group, and others but does not specifically add execute permission for all. Therefore, the command that adds execute permission for everyone to file5 is the most appropriate and effective choice.