"It is a great loss for the Argentinian people."
Translation:Es una gran pérdida para el pueblo Argentino.
gente de Argentino is grammatically incorrect. There is no place called Argentino. You can say gente de Argentina = people from Argentina, but it's not what is asked in this exercise. You can also say gente Argentina = Argentinian people (people here is the pluriel of person). Remember that gente is a feminine noun, so it must be followed by feminine adjective.