untenable
adjective /ʌnˈtenəbl/
  /ʌnˈtenəbl/
(formal)- (of a theory, position, etc.) that cannot be defended against attack or criticism- His position had become untenable and he was forced to resign.
- He found no one to support his largely untenable views.
 Oxford Collocations DictionaryUntenable is used with these nouns:- situation