How was the periodic law rearranged to become the periodic table, and what is its purpose?

At earlier times elements were arrangrd on the basis of their atomic masses to study their properties easily but there were various problems like isotopes needs different position in perodic table.

After discovery of atomic number modern periodic table was created on the basis of atomic number (number of proton) that is unique for each element and varies regularly. So study of a group of elements is much easier than each element seperately that is why modern periodic table was formed.

Explanation:

14,16 18 reacts with group

the answer is d. 74.02