Which of the following is an antonym of "mandatory"?

The term "mandatory" refers to something that is required or obligatory, meaning it must be done. An antonym would therefore represent the opposite concept. The word "optional" fits this definition perfectly, as it signifies something that is not required and can be chosen at the discretion of the individual. In contrast, "compulsory," "obligatory," and "required" all connote a sense of necessity or duty, aligning closely with the meaning of "mandatory." This makes "optional" the correct choice, as it conveys a sense of choice rather than compulsion.