Here's one question-

What is the total number of electrons in an atom with highest principal quantum number as 4?????????

Such an atom shows electronic configuration ...4f¹⁴5d¹6s² and the differentiating electron enters ante penultimate 4f orbital. So, the atom is Lutecium with atomic number 71.

The last element of 4th period with heighest atomic number is with atomic number 36 is not the answer.

see frnd...........for principal quantum no. 4 the azimuthal quantum numbers r such:   

                                l=0(4s)

                                l=1(4p)

                                l=2(4d)

                                 l=3(4f)......so  heres a formula:NO. OF ELECTRONS IN A GIVEN SUB ENERGY LEVEL

                                                                      =2(2L+1)

FINDING IT::FOR l=0 SO  2(2*0+1)====2ELECTRONS(IN THE SAME WAY CALCULATE FOR OTHER SUBENERGY LEVELS   .....THEN ADD THEM THEY WILL BE LIKE 2+6+10+14=32)SO THERE R 32 TOTAL NO. OF ELECTRONS IN FULL PRINCIPAL QUANTUM NO.4)

hope u got it........!!!!!