Question

Mendeleev's periodic table is based upon the atomic masses. This periodic table is upset by the fact that

• A. many elements have several isotopes
• B. noble gases do not form compounds
• C. some groups are divided into two sub groups A and B
• D. atomic weights of elements are not always whole numbers

Answer 1

The correct option is A

many elements have several isotopes

The explanation of the correct option:

• In the Periodic table, there are many elements that have several isotopes. At that time it was difficult for Mendeleev to arrange the isotopes of many elements because isotopes have similar chemical properties but different atomic masses.
• Eg. The element chlorine has two isotopes, C-35 and C-37, having atomic masses of 35 and 37, respectively.

The explanation of the incorrect option:

• Noble Gases: Noble gases were discovered very late because they are very inert and present in extremely low concentrations in our atmosphere. They were placed in a new group without disturbing the existing order.
• Some groups of Mendeleev's periodic table are divided into two subgroups A and B without any problem.
• In Mendeleev's periodic table, Atomic weights of elements are not always whole numbers.

So, the correct option is A, This periodic table is upset by the fact that many elements have several isotopes.