Question 1 How could the modern periodic table remove various anomalies of Mendeleev’s periodic Table ?

(i) The modern periodic table is based on atomic number, while Mendeleev’s periodic table was based on atomic mass. (ii) The isotopes of an element have same number of protons (or atomic number). So they are alloted the same position in modern periodic table. (iii) Cobalt and nickel are placed at 9th and 10th position respectively. (iv) Hydrogen has been alloted special position, i.e., it is placed at the top of alkali metals in the first group.