A change or choice between two or more things.

विकल्प

English Usage: He had to choose between the two altern.

Hindi Usage: उसे दोनों विकल्पों में से चुनना था।

To change back and forth.

बदलना

English Usage: They will altern their roles each week.

Hindi Usage: वे हर हफ्ते अपनी भूमिकाएँ बदलेंगे।

Rooms or items that can be used in place of one another.

विकल्पीय

English Usage: The altern options are just as good as the original.

Hindi Usage: विकल्पीय विकल्प मूल के समान अच्छे हैं।