State the Modern Periodic Law

(i) State Modem Periodic Law.
(ii) How many:
(a) groups and
(b) periods are present in the modern periodic table ?
(iii) State how the problem of placing:
(a) hydrogen,
(b) isotopes of an element has been solved in this periodic table

(i) The properties of elements are the periodic function of their atomic numbers.
(ii) (a) 18 groups (b) 7 periods (in) (a) Hydrogen in 1st group.
(b) Isotopes of an element at one place