You are right. I don't understand instructions in 100%. I correct solution.

I've added a extra testcase for even length words.
Thanks for the feedback.

The soloution from user bryjamus managed to pass. So test cases like "abca" are missing. Where first and last letter are the same but is still not a palindrome.

public static bool IsPalindrome(string w)
{
var arr = w.ToLower().ToArray().Where(x=>Char.IsLetter(x));
return arr.First() == arr.Last();
}

That will return wrong answer if the first and letter charater are the same, and the letters after that is not a palindrome.
Like "abca" return true where it should return false.