Use suitable prefixes to form antonyms:
A prefix is an affix which is placed before the stem of a word. Adding it to the beginning of one word changes it into another word. Prefix – In-, Un-, Im-, Dis-
Gratitude
Certain
Install
Personal
Honour
Disputed
Correct
Mask
Lawful
Grateful
Wavering
Regard
Perturbed
Tolerant.