Answer
See the answer below.
Work Step by Step
From definition: $0\leq\ell\leq n-1$ and $-\ell\leq m_\ell\leq \ell$.
a) $n=4, \ell=2$ means 4d subshell and $m_\ell=-1$ means it's the second in energy level.
b) From definition $n^2=25$ orbitals, $n-1=4$ subshells labeled s, p, d, f and g.
c) From definition $2\ell+1=7$ orbitals per subshell, with $-3\leq m_\ell\leq3$
