as given in the last years board paper set 31/2 Q.no. 16

The question is not clear about slots. Assuming it refers to positions in periodic table, her's the answer:

However, if we have to  place the two isotopes in modern periodic table, we will place them in the same slot as the modern periodic table is based on increasing atomic number and not atomic mass.

Ifif we have to  place the two isotopes in Mendeleev's  periodic table, we will place them in different slots as the Mendellev's periodic table is based on increasing atomic mass and not atomic number.