Electron in an atom is characterized by four quantum numbers. Number of electrons with  l=0, m=0 in  Cr (Z= 24) atom are

l=0 means s-subshell.Cr- 1s22s22p63s23p64s13d5. Number of s- electrons are 7For l=0, m=0 ;Thus  7 s-electrons are present, all will have m=0 ;