Question

Why isotopes are placed in same position in the piriodic table?

Answer 1

In periodic table elements are placed on the basis of atomic number. As isotopes are atoms of same element having same atomic number but different mass number, so they have same position in the periodic table. 

Answer 2

in preodic table atoms are arranged in order of their increasing atomic number.

isotopes are placed in same position in preodic table because isotopes differ in their mass number not in their atomic number.....