Question

prevailing torque (lock) nuts should be replaced rather than reused after removal because: the locking material is deformed the threads are damaged the law requires it can be reused with a lock washer

Explanation:

Prevailing - torque (lock) nuts have locking material which gets deformed upon removal, reducing their locking effectiveness. Threads may not necessarily be damaged, and it's not a legal requirement. Using a lock - washer doesn't make up for the loss of the nut's original locking function.

Answer:

The locking material is deformed