Question

Assertion (A): Mendeleev failed to explain the position of isotopes in his periodic table.​
Reason (R) : Isotopes have different atomic mass.​

• A. Both (A) and (R) are true, but (R) is not the correct explanation of the (A). ​
• B. Both (A) and (R) are true, and (R) is correct explanation of the (A)​
• C. (A) is false, but (R) is true.​
• D. (A) is true, but (R) is false.​

Answer 1

The correct option is B Both (A) and (R) are true, and (R) is correct explanation of the (A)​

Mendleves classified the elements on the basis of increasing atomic masses. So accordingly isotopes should have been assigned different positions but in his table there was no position assigned for isotopes. So it became the limitation of his periodic table that he was not able to explain the position of isotopes.