The first one is okay, the second one doesn't make much sense because weekends have two days, so if you say "on weekend morning" you'd be referring specifically to the last weekend but wouldn't specify if Saturday or Sunday.

Correct answer: 1) on a weekend morning When a Russian or Ukrainian speaker has any doubts about whether to use an article or not, 80%+ of the time, the answer is "yes, use that article." Articles don't exist in these two languages, so most Russian and Ukrainian speakers use too few articles in English, rather than too many articles ;)

Hello! I would agree that 1) "on a weekend morning" would be better especially if you are differentiating between "a weekend morning" and a "weekday morning". But an even better way of writing it would be "on a morning during the weekend" which indicates that it could be Saturday or Sunday morning. I hope that helps!