(a) The four quantum numbers are:
(i) Principal quantum number (n)
(ii) Azimuthal quantum number (l)
(iii) Magnetic quantum number (m )
(iv) Spin quantum number (m )
(b) The argument of student 1 is correct. If there are two electrons in the same subshell the first three quantum numbers become the same. Hence we need fourth quantum number to identify the electron.
(c) n = 3, l = 0, m = 0, s = +½