"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.
I came across this a while ago..."grande" is one of those adjectives that actually changes meaning if it's before or after the noun. If you say "pérdida grande", it means "large loss", while "gran pérdida" means "great loss".