The number of revolutions made by an electron in one second around the nucleus in the 4th orbit of hydrogen atom is approximately

Time taken for one revolution =1.5×10-16n3z2 seconds  Numberofrevolutions sec=11.5×10-16n3z~2                                      =z2n3×6.6×1015given n = 4        Z = 1∴ Numberofrevlutions sec=1243×6.6×1015                                          = 0.1 × 1015                                            = 1014