Final answer:
After executing 'chmod 600 sample', the file or directory named 'sample' becomes readable and writable only by the owner, with no permissions for the group or others.
Step-by-step explanation:
The question relates to Unix/Linux file permissions and the use of the chmod command. When the chmod 600 sample command is executed on a directory (or a file), it sets the permissions such that the file becomes readable and writable only by the owner. The numbers in the command represent the permissions: '6' for the owner (read (4) + write (2)), and '0' for both the group and others, meaning no permissions for them.
The correct answer to the question is therefore: b) The file becomes readable and writable only by the owner.