"Who is weakest" was not accepted; feel this is a bit persnickety, the article is implied in this statement.
Thanks! I was copying the name of the Tv show and clearly forgot (when adding on the 'kto jest') to change the case. A typical error of a 'young' Polish learner.
I just remembered that one time when I was watching it, the women taking part in the show (and the host was also a woman, a well-known feminist in fact) decided to eliminate the only guy, so instead of saying "Jesteś najsłabszym ogniwem" the host said "Michale, jesteś mężczyzną... do widzenia." :D