You are correct that this solution would throw an exception if an id was passed in that was not a valid planet id (like 13, since there are not 13 planets), but the description does not state what should happen in such a case and there are no test cases for such a case that I am seeing. It may be considered good practice to throw a clearer exception with a message stating what is wrong instead of just letting C# throw an out of bounds error for me, but I tend to prefer shorter solutions and definitely think throwing an exception for invalid inputs is generally appropriate.

am i forgetting things here? i was thinking that return could give you and error if the id was bigger than the
size of the array.
Or there is something im not seeing here?

clever as clever can get