Mixed-gender group in German?

you could use the male form:

"die Studenten"

(that was usually done, but nowadays some feminists think they are not meant too and think it is a discrimination if the female form is not noted also, so)

you could use the male /and/ female form:

"die Studenten und Studentinnen"

(especially when addressing a group of people this is the usal form, sometimes this is not practial e.g. in large articles where they are noted often noted, the text gets annoying to read, but)

you could use (the imho very annoying) the Binnen-I:

"die StudentInnen" (a capitalized i to show that both "Studenten" and "Studentinnen" are meant)

(note that some would-be innovative and would-be tolerant /modern/anti-discrimination/fill in something... newspapers etc. use that all over the place and articles get nearly ununderstandable by that, because they use it for every other word and it breaks up the text flow in my personal opinion).

if there is you could use an alternative form, like for "Studenten" (note that for many words you won't find an alternative form that is still viewed gender neutral in plural, though as said, that is what it was in the past)

"die Studierenden" (plural of "der Studierende")

(note that if you do that you might be condemned by self declared feminists that you did not direct it to the female students too)

Goddess of Gramar is right!

You can say "Studierende" (more formal way) or "Studentinnen und Studenten", but also "Studenten" is possible. If I use the word mixed-gender group of students I would take "Studenten"!

Greetings from Germany!

In speaking, usually "Studenten und Studentinnen" (or the reverse), unless you won't offend someone with just "Studenten". In writing, you'd often see StudentInnen. Easiest would be Studierende.