The correct sequence of filling of electrons in n=6 is:

Step-by-step solution

According to the Aufbau principle, electrons are filled in orbitals in the increasing order of their (n+l) values. For a given shell n , the orbitals are ns , (n-2)f , (n-1)d , and np . Calculating the (n+l) values for n=6 : For 6s : n=6, l=0 , so n+l = 6+0 = 6 . For 4f : n=4, l=3 , so n+l = 4+3 = 7 . For 5d : n=5, l=2 , so n+l = 5+2 = 7 . Since n is smaller for 4f than 5d , 4f is filled before 5d . For 6p : n=6, l=1 , so n+l = 6+1 = 7 . Since n+l values are equal for 4f, 5d, and 6p , the orbital with the lowest n