Answer :
since they are students order is not going to matter and it will be a combination.
[tex]nCr=\frac{n!}{r!(n-r)!}[/tex]n= total of students
n=19
r= students per group
r=3
[tex]\begin{gathered} 19C3=\frac{19!}{3!16!} \\ 19C3=969 \end{gathered}[/tex]there can be formed 969 groups