Science 1 Test 5 :- Dr. Mujawar Sir

Explanation
Mendeleev's periodic table consists of 8 groups. The groups in the periodic table are vertical columns that contain elements with similar chemical properties. Each group is labeled with a number and sometimes a letter to indicate its specific characteristics. Mendeleev's periodic table is organized based on the atomic number and the arrangement of elements in increasing order of atomic number. Each group represents a specific configuration of valence electrons, which determines the chemical behavior of the elements within that group. Therefore, the correct answer is 8.

Explanation
Mendeleev's Periodic Table is based on atomic mass. Mendeleev arranged the elements in order of increasing atomic mass and observed that certain properties repeated at regular intervals. This led to the development of the periodic table, where elements with similar properties were grouped together. Although the modern periodic table is based on atomic number, Mendeleev's original table was based on atomic mass.

Explanation
During the time of Mendeleev, a total of 63 elements were discovered. Mendeleev's periodic table, which he published in 1869, included these 63 elements arranged in order of increasing atomic weight. This table provided a framework for understanding the properties and relationships between different elements, and it also allowed for the prediction of the existence and properties of undiscovered elements.

Explanation
Eka-Boron is a term used to describe an element that is predicted to have similar properties to Boron but has not yet been discovered. Scandium is the element that fits this description, as it is located directly below Boron in the periodic table and has similar chemical properties. Therefore, Scandium is the correct answer.

Explanation
Cobalt and Nickel are placed in the same place in Mendeleev's table because they both belong to the same group, which is Group 9. In the periodic table, elements in the same group have similar chemical properties and exhibit similar behaviors. Therefore, Cobalt and Nickel share certain characteristics and are placed together in the same location.

Explanation
The merit of Mendeleev's Periodic Table is the inclusion of a dedicated place for Noble Gases. Mendeleev recognized the unique properties of these elements and their lack of reactivity, which did not fit into any existing group. By creating a separate group for Noble Gases, Mendeleev's periodic table provided a more comprehensive and organized representation of the elements, allowing for a better understanding of their properties and trends.

Explanation
The demerit of Mendeleev's Periodic Table is the placement of Hydrogen. Mendeleev initially placed Hydrogen in a separate group, but its properties do not match those of the elements in that group. Hydrogen can exhibit properties of both metals and non-metals, making its placement in the periodic table ambiguous. This inconsistency in the placement of Hydrogen is considered a demerit of Mendeleev's table.

Explanation
Hydrogen wants to be placed in group 1 and 7 because it has one electron in its outermost shell, similar to the elements in group 1, and it can also gain one electron to achieve a stable configuration, similar to the elements in group 7. Therefore, hydrogen exhibits properties of both group 1 and group 7 elements.

Explanation
In Mendeleev's Periodic Table, Group 7 belongs to the Halogen family. Halogens are highly reactive nonmetals that have 7 valence electrons, making them one electron short of a stable octet. They include elements such as fluorine, chlorine, bromine, iodine, and astatine. These elements readily form compounds with other elements, especially alkali metals, to achieve a stable electron configuration. Therefore, Group 7 is correctly identified as the Halogen family.

Explanation
The horizontal rows in Mendeleev's Periodic table are called "Periods." Each period represents a different energy level or shell of electron orbitals. The elements within a period have the same number of electron shells. As you move from left to right across a period, the atomic number increases, indicating an increase in the number of protons and electrons. The properties of elements within a period gradually change from metallic to non-metallic as you move across the table.