Which of the following statement is correct in regard to the classification of elements ?

(a) Elements in the periodic table are arranged on the basis of increasing atomic masses   
(b) Elements in Mendeleev’s periodic table are arranged on the basis of increasing atomic numbers
(c) In modern periodic table, the element nickel of lower atomic mass is kept before the element cobalt of higher atomic mass
(d) In modern periodic table, the isotopes of chlorine having diffrenet atomic masses are kept in the same group.

Correct answer: (d) In modern periodic table, the isotopes of chlorine having diffrenet atomic masses are kept in the same group.

Explanation: The isotopes of chlorine, Cl-35 and Cl-37, having different atomic masses but same atomic numbers are kept in the same group in the modern periodic table.