Chemistry Test 217

Eka-aluminium and gallium are the same elements because the properties of Eka-Aluminium are almost identical to the qualities of the gallium element. Eka-Aluminium is a chemical element that has nearly identical properties to the gallium element. The properties of the elements, such as their atomic mass, density, melting temperature, the formula of chloride, and the formula of oxide, are nearly identical to those anticipated by Mendeleev in his theory.

Group number eighteen. This suggests the presence of a Chalcogens element. Chalcogens elements are found in Group 16 of the modern periodic table, which is the most recent revision. Thus, the element having electronic configuration 2, 6 would be found in group 16 of the Modern Periodic Table, according to this definition. Therefore, option (C) is the most appropriate choice.

Potassium belongs to a group - (1) and period - (IV) of the periodic table. Hence among the given options, Potassium has a maximum atomic radius.

Carbon and Nitrogen belong to the period - (II) of the periodic table and on the right side hence it is obvious that atomic radii of Carbon and Nitrogen are very much small than Sodium and Potassium.

Sodium and Potassium belong to a group - (1) and  Potassium is placed below Sodium hence the atomic radius of Potassium more than Sodium.

BF₃ - Trigonal planar with bond angle 120^º.

PCI₅ - Trigonal bipyramidal with bond angles 120^º and 90^º.

The correct answer is C-12.

The International Union of Chemists selected the most stable carbon isotope (C-12) or ¹²C as the standard for comparison of the atomic masses of various elements.

The mass of C-12 is taken as a 12 atomic mass unit (standard).

A Carbon-12 contains six protons, six neutrons, and six electrons.

The ionic size increases with the addition of electrons and decreases with the removal of electrons. S²⁻ has the largest size due to the highest electron repulsion among the given species.

Carbon has atomic number 6, so it has six electrons. The ground-state electronic configuration is 1s² 2s² 2p².

An excited state is produced when an electron is promoted to a higher orbital without changing the total number of electrons; this is not ionisation (loss of an electron).

Promoting one electron from the 2s orbital to the 2p orbital gives the configuration 1s² 2s¹ 2p³, which corresponds to option B.

Mendeleev himself added these elements to the periodic chart in 1902 as group 0 elements, without altering the fundamental principle of the periodic table in the process. Alfred Werner, a Swiss chemist, was the first to solve the dead zone of Mendeleev’s table, which was discovered in 1905. He came to the conclusion that the rare-earth elements (lanthanides), of which there were 13 known, were contained within that gap.