Alternate & Alternative

Alternate means occurring by turns; succeeding each other, take turns, change (verb): “He and his wife alternate turns for cleaning the house.” It also means ‘one and then the other; every other, successive’: “Each of the two brothers works in the shop on alternate Sundays.” / “The shirt had alternate red and white stripes.”
The third meaning for alternate is standby, backup, understudy (noun): “Military bosses always keep an alternate plan in mind while planning an operation.”
alternative implies a choice between two or among more than two things; something remaining to be chosen; an option: “Is there an alternative to going?”
“If he wants to get to Mumbai by tonight, he has no alternative but to go by plane.”
Keep in mind the distinction between the two words: alternate implies the taking of turns, while alternative implies a choice.