Consider the following elements: Be, Li, Na, Ca, K. Name the elements of (a) same group (b) same period.

(a) Name an element whose properties were predicted on the basis of its position in Mendeleev's periodic table.

(b) Name two elements whose atomic weights were corrected on the basis of their positions in Mendeleev's periodic table.

(c) How many elements were known at the time of Mendeleev's classification of elements?

What is the main characteristic of the last element in each period of the Periodic Table? What is the general name of such elements?

What is meant in the periodic table by :

(a) a group, and

(b) a period?