You Can Choose to Do It If You Want, Not Obligatory
This page is the CodyCross answer for the clue below from Science Lab, Group 313, Puzzle 5 (Vaporization).
Question is: You Can Choose to Do It If You Want, Not Obligatory
and the answer is: OPTIONAL
Word Meaning:
OPTIONAL — Not compulsory; left to personal choice; elective.
Definitions from Wiktionary.