What is the 3rd Element in periodic table?
(a) What is the main characteristic of the last elements in the periods of the periodic table? What is the general name of such elements?
(b) What is the number of elements in (a) 1st period, and (b) 3rd period, of the modern periodic table?
The atomic number of an element is 20. In the modern periodic table, this element is placed in :
(a) 2nd period (b) 4th period (c) 3rd period (d) 1st period
What is the number of elements in the 1st and 3rd period of the modern periodic table ?