Question

In the modified Mendeleev periodic table,_____ groups and ____ periods are present, whereas in the modern periodic table,_____ groups and ____ periods are present, respectively:
(A) 9,8,18,7
(B) 7,9,18,7
(C) 9,7,18,8
(D) 8,7,18,7

Answer 1

Hint: The modern periodic table is a table that contains all the elements grouped together according to their atomic numbers or similar properties. The periodic table by Mendeleev contains all the elements arranged by the atomic masses.

Complete step by step solution:
-Modern periodic table is based on atomic number. Elements are arranged in increasing order of atomic mass. Elements having the same valence shell were placed in the same period while elements having the same number of valence electrons were placed in the same period.
-Mendeleev's periodic table is based on atomic mass. Elements are arranged in increasing order of atomic mass. Elements having similar properties were placed directly on one another.
-Differences between Mendeleev's Periodic table and Modern periodic table:

Mendeleev's periodic table	Modern Periodic table
1. According to Mendeleev theory, The physical and chemical properties of elements are a periodic function of their atomic masses.	1. Modern periodic law states that the properties of elements are a periodic function of their atomic numbers.
2. The basis of classification was the formula of hydrides and oxides made by the elements.	2. The basis of classification is the electronic configuration of the elements.
4. The noble elements were not included in the table, as they were not discovered at that time.	4. Modern periodic table included noble elements in group 18 as a last and separated group.
5. It has an ambiguity in the position of some elements as, some elements with larger atomic weights are placed before elements with smaller atomic weight without any justified reason.	5. Here, all are arranged systematically with increasing atomic number and weight too.
6. According to this theory, the isotopes with different atomic weights should be placed in different positions, but are not given any position and no, justified reason was explained.	6. The isotopes were assigned the same position as they have the same atomic number.
7. Some different elements were grouped together while some similar elements were placed in different groups. Ex: alkali metals like Li, Na, K were placed with coinage metals Cu, Ag, Au etc.	7. No such confusion, the coinage metals have their own position in d-block and alkali metals are placed in s-block elements.
8. Group VIII has three elements together, like Fe, Co, Ni	8. These elements are placed in different groups, under d-block elements.

-There are a total of 8 groups and 7 periods in the modified Mendeleev table.
-There are a total of 18 groups and 7 periods in the modern periodic table that is followed worldwide now.

Clearly, the answer is (D).

Note: The Mendeleev periodic table had many disadvantages.He was unable to locate hydrogen in the periodic table. Increase in atomic mass was not regular while moving from one element to another. Later on, isotopes of elements were found which violated Mendeleev's periodic law. Thus, the modern periodic table was accepted to conquer these ambiguities.