Which defect on Mendeleev periodic table is automatically overcome by shifting the basis from atomic number?
A.Placing coinage metals with alkali metals
B.Position of isotopes
C.Position of hydrogen
D.All the above

Hint: In Mendeleev’s periodic table, the elements are arranged on the basis of fundamental property, atomic mass and chemical properties. During Mendeleev’s work only elements were known. Moreover, he arranged the elements such that the elements with similar properties fell into the same vertical columns of the periodic table.

Complete step by step answer:
Dmitri Ivanovic Mendeleev, a Russian chemist was one of the most important contributors to the early development of the periodic table. However, many periodic tables were made during that time but the most important one was the Mendeleev’s periodic table.
Moreover, in his periodic table, the vertical columns and horizontal rows were named as groups and periods respectively. He observed that the elements were arranged in the increasing order of atomic masses and there was periodic occurrence of elements with similar properties.
So, based on these observations, he formulated the periodic law which says that the properties of elements are the periodic function of their atomic masses.
Moving further, there were many defects in Mendeleev’s periodic table. One such defect was the position of isotopes. It states that the isotopes of the element must be given separate places in the periodic table because they have different atomic masses. However, as isotopes have the same atomic number, so they should have the same places in the periodic table. Thus, this drawback was easily overcome.

Hence, option B is correct.

Note:
Some gaps in the Mendeleev’s periodic table were left for the elements yet to be discovered. Thus if a certain new element is discovered, it can be placed in a new group without disturbing any existing group. So, this was basically a merit of this table.