Can you tell me, how many eggs an average chicken lays in an year?
Sure! Depending on the breed a an average chicken can lay anywhere from 150 up to 300 eggs in an year.

Note that these are for commercial breeds of chickens, which have been bred to lay a lot of eggs.
Wild chickens on the other hand only lay between 10 to 15 eggs.

Hence, in summary, it highly depends on the breed of the chicken, which determines how many eggs it will in an year.

Sources: 
https://grow.ifa.coop/
https://birdfact.com/articles/how-often-do-chickens-lay-eggs
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