Which of the following statements is true?

i. For enabling primary key constraint, ALTER TABLE is used. ii. For enabling primary key constraint, ENABLE keyword is used all alone. iii. For disabling primary key, index will be dropped. iv. For disabling primary key, index will not be dropped.

This answer is correct because for enabling primary key constraint, ALTER TABLE is used followed by ENABLE key word. Similarly, for disabling primary key constraint, index will be dropped because the index comes along with primary key by default and since primary key constraint is not applied on the records, the index is also dropped.