b)Principal quantum number is number which determines the main energy level or shell in which the electron is present.It gives the average distance of the electron from the nucleus & specifies the value of the energy of the electron.

Azimuthal quantum number is the number which determines the sub shell in a principal energy shell to which an electron belongs.

In the periodic table each period begins with the filling of principal quantum number (n). The value ofnfor the sixth period is 6. For n= 6, azimuthal quantum number (l) can have values of 0, 1, 2, 3, 4.

In the 6thperiod, electrons can be filled in only 6s, 4f, 5d,and 6psubshells. Now, 6s has one orbital, 4f has seven orbitals, 5d has five orbitals, and 6p has three orbitals. Therefore, there are a total of sixteen (1 + 7 + 5 + 3 = 16) orbitals available.

According to Pauli’s exclusion principle, each orbital can accommodate a maximum of 2 electrons. Thus, 16 orbitals can accommodate a maximum of 32 electrons.

Hence, the sixth period of the periodic table should have 32 elements.

a)Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to caesium and francium which are the least electronegative at 0.7.