Ans.
1. Mendeleev was the first scientist to successfully classify all known elements.
2. Mendeleev's periodic table helped to revise the atomic masses of some elements to give them proper places in the periodic table based on their properties.
For Example, the atomic mass of beryllium (Be) was corrected from 14.09 to 9.4 and it was placed before boron (B).
3. Mendeleev's periodic table left some vacant spaces in it for elements which were not discovered that time.
Three of the unknown elements he named as eka - boron, eka - aluminium and eka - silicon. These elements were later discovered and named as scandium (Sc), gallium (Ga) and germanium (Ge), respectively.
4. There was no place reserved for noble gases in Mendeleev's original periodic table. But, when noble gases were discovered later, Mendeleev placed them in a new group called as 'zero group' without disturbing the position of other elements.
