Periodic Classification of Elements

The properties of an element depend on the valence electrons or the number of electrons in the outermost orbit. In a group of modern periodic table, all the elements have the same number of valence electrons. For example, all alkali elements have one electron in their outermost orbit. Hence, they have similar properties.

As per the definition of the modern periodic law stated by Mosely, the physical and chemical properties of elements are the periodic functions of their atomic numbers. Hence, the third option is correct.

In the modern periodic table, the elements are arranged in the increasing order of their atomic numbers. The number of electrons in an atom are equal to its atomic number. Hence, there is a gradual change in their electronic configuration.

Potassium belongs to the fourth period whereas the remaining elements belong to the third period.

Metals have 1, 2 or 3 electrons in their outermost orbit and non-metals have 5, 6 or 7 electrons in their outermost orbit. The electronic configurations of A, B, C, D and E are 2, 8, 4; 2, 8, 5; 2, 8, 7; 2, 8, 8; and 2, 8, 8, 1, respectively. As the element C has 7 electrons in its outermost orbit as compared to 5 electrons in element B, so it is more non-metallic. Hence, option (3) is the correct answer.

The second period in the modern periodic table consists of the elements lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon, in that order. The given elements belong to the second period. As we move from left to right of a period, the atomic size decreases. Hence, the first option is correct.

Elements of group 1 are alkali metals. They are lustrous solids with low density and low melting points. They react vigorously with cold water to form alkalis. Hence, option (1) is the correct answer.

Ionisation potential is the energy required to remove one or more electrons from the outermost orbit of an isolated gaseous atom. The smaller the size of the atom, the more difficult it becomes to remove the valence electron due to the attraction of the nuclear charge on the electrons.

Ionisation potential increases as we move from the left to the right of a period and decreases as we move down a group. Sodium is on the extreme left of period 3. Hence, it has the least ionisation potential as compared to the elements of the first three periods.

In the modern periodic table, the first period has 2 elements, the second has 8 elements and the third also has 8 elements. The electronic configuration of ‘A’ is 2, 2 and the electronic configuration of ‘B’ is 2, 8, 2. In a neutral atom, number of protons is equal to the number of electrons. Hence, ‘A’ will have 8 protons less than 'B'.

The third period in the modern periodic table consists of the elements sodium, magnesium, aluminium, silicon, phosphorous, sulphur, chlorine and argon, in that order. The given elements belong to the third period. As we move from left to right of a period, the ionisation potential increases. Hence, sodium has the least ionisation potential and chlorine has the highest. So, the fifth option is correct.

As the elements with noble configuration have completely filled valence shells, they neither accept electrons nor lose electrons. Hence, they have 0 electron affinity.

The element in question is aluminium as it has the electronic configuration 2, 8, 3. This metal is amphoteric in nature; it reacts with both acids and alkalis. Hence, its oxide and hydroxide are amphoteric in nature.

The tendency of an atom to attract electrons towards itself when combined in a compound is called electronegativity. If the difference in electronegativity values between the combining atoms is more, then the chemical bond formed between them will be electrovalent. If the difference in electronegativity values between the combining atoms is less, then the chemical bond formed between them will be covalent.

When an atom accepts an electron, the anion is larger than its parent atom because the nuclear charge gets distributed over more electrons than earlier. Similarly, when an atom loses an electron, the cation is smaller than its parent atom because the nuclear charge gets distributed over fewer electrons than earlier.  Hence, the correct option is (2).