Why are the elements of the fourth, fifth and sixth stages in Mendelee

1.	Why are the elements of the fourth, fifth and sixth stages in Mendeleev's periodic table divided into a pair and a pair of series?
Answer» Answer: 1)There are 9 groups(0 , 1 , 2 ,3 , 4 , 5 , 6 , 7 , 8) and 7 periods. 2)Groups 1 to 7 have been DIVIDED into two subgroups - A and B. 3) group zero consist of NOBLE gases . 4)Group 8 consist of 9 elements which are arranged in 3 triads. Explanation:

Why are the elements of the fourth, fifth and sixth stages in Mendeleev's periodic table divided into a pair and a pair of series?

Answer»

Answer:

1)There are 9 groups(0 , 1 , 2 ,3 , 4 , 5 , 6 , 7 , 8) and 7 periods.

2)Groups 1 to 7 have been DIVIDED into two subgroups - A and B.

3) group zero consist of NOBLE gases .

4)Group 8 consist of 9 elements which are arranged in 3 triads.

Explanation: