It is the energy required to remove an electron from an isolated gaseous atom in its ground state.
M(g) + I.E. ⟶M⁺ (g) + e^-

The elements of group 1 (alkali metals), group 2 (alkaline earth metals) and group 13 to 17 constitute the representative elements. They are elements of s-block and p-block.

Ar, K⁺, Cl^- S^2-, or P^3- are isoelectronic with ca²⁺.

(i) s-Block elements: ns^1-2 where n = 2 - 7.
(ii) p-Block elements: ns² np^1-6 where n = 2 - 6.
(iii) d-Block elements: (n -1) d^1-10ns^O-2 where n = 4 - 7.
(iv) f-Block elements: (n - 2)f^0-14 (n - 1) d^0-1 ni where n = 6 - 7

(a) Silicon is group 14 element with a valence of 4; bromine belongs to the halogen family with a valence of 1. Hence the formula of the compound formed would be SiBr₄.
(b) Aluminium belongs to group 13 with a valence of 3; sulphur belongs to group 16 elements with a valence of 2. Hence, the formula of the compound formed would be Al₂S₃.

The given nom-metals are arranged in the increasing order of non-metallic character as follow

Na⁺ and Ne are isoelectronic species. However, the nuclear charge in Na⁺ is more than in Ne. Hence, the electrons are more tightly held in Na⁺ and it has higher ionisation enthalpy. 

The ionisation enthalpy of the main group elements decreases regularly on moving down the group due to the following two factors.
(i) Atomic size On moving down the group,atomic size increases due to the addition of new higher energy shell.As a result of this, forces of attraction of nucleus for valence electrons decrease and ionisation enthalpy also decreases.
(ii) Screening effect On moving down the group, screening effect or shielding effect increases, so ionisation enthalpy decreases (because forces of attraction between nucleus and electron secreases).

On moving down the group, electronegativity decreases because atomic size increases. Fr has the largest size, therefore it is least electronegative.

Atomic radius of F is expressed in terms of covalent radius while, atomic radius of neon is usually expressed in terms of van der Waals' radius. van der Waals' radius of an element is always large than its covalent radius.
Therefore, atomic radius of F is smaller than atomic radius of Ne (F = 72 pm, Ne = 160 pm)

Electronic configuration of Na and Mg are
Na = 1s², 2s², 2p⁶, 3s¹ and 1s², 2s² , 2p⁶, 3s². 
Second ionisation energy of Na is higher of because it acquires nearest noble gas configuration after losing one electron and second electron is to be removed from the noble gas configuration.

Elements of second group are known as alkaline earth metals ( Mg, Cs, Sr, Ba, etc. ). Their general electronic configuration for valence shell is ns^2. These elements can form dipostive cations by the loss of two electrons easily.

From Table 

the roots for 1, 2 and 0 are un, bi and nil, respectively. Hence, the symbol and the name respectively are Ubn and unbinilium.

Chemical and many physical properties of the elements depend on the electronic configuration of the atoms, whereas the nuclear properties do not.

The basic theme of organisation in the periodic table is to simplify and systematise the study of physical and chemical properties of all the elements and their innumerable compounds.

Factors affecting Ionization enthalpy.
(i) Atomic size. With the increase in atomic size, the number of electron shells increases and thus the force of attraction between the electrons and the nucleus decreases. Therefore the ionization enthalpy decreases.
(ii) Nuclear charge. As the nuclear charge increases the attraction for the electron also increases that's why ionization enthalpy increases.
(iii) Screening or shielding effect. In a multi-electron atom, the electron present in the inner shells shield the electrons in the valence shell as a result these electrons experience less attraction from the nucleus. This leads to lesser ionization enthalpy.
Variation along a period. On moving from left to right in a period the nuclear charge increases and the atomic size decreases as a result ionization enthalpies are expected to increase.
Variation within a group. On moving down the group as the atomic size of the elements increases that's why ionization enthalpy decreases down the group

(i) Group 1 elements are most reactive.
(ii) Group 18 elements are least reactive because they have stable electronic configuration.
(iii) It may cause high blood pressure and any other harm to the body. It disturbs the person physically and mentally also.
(iv) They are cool, calm, happy and help other people. They are more healthy than aggressive people.
(v) aggressive people pick up fight. They do not accept their fault. Sometimes, it leads to physical injury which put them in trouble. We should not involve in such act.

(i) No, it is not a good idea to remain alone.
Advantages
(a) The person does not bend under peer pressure.
(b) The person can do his work peacefully and remain attentive in the class which may help to get success.
Disadvantages
(a) It makes the person tensed due to low social interaction.
(b) Person becomes self-centred.
(c) Interaction with other helps to increase knowledge and increases tolerance.
(ii) She has values like cooperation, tolerance, respecting each other's work and ideas. She is more successful than the person working alone.
(iii) It is because it has lowest ionisation enthalpy and higher polarising power.

There are numerous physical properties of elements such as melting points, boiling points, heats of fusion and vaporisation, energy of atomisation, etc., which show periodic variations. The cause of periodicity in properties is the repetition of similar outer electronic configuration after certain regular intervals. e.g. all the elements of 1s group (alkali metals) have similar outer electronic configuration, i.e. ns¹.
₃Li = 1s², 2s¹
₁₁Na = 1s², 2s², 2p⁶ , 3s¹
₁₉K = 1s², 2s², 2p⁶ , 3s², 3p⁶, 4s¹
Therefore, due to similar outermost shell electronic configuration all alkali metals have similar properties. e.g., sodium and potassium both are soft and reactive metals. They all form basic oxides and their basic character increases down the group. They all form unipositive ion by the loss of one electron. Similarly, all the elements of 17th group (halogens) have similar outermost shell electronic configuration, i.e. ns²  np⁵ and thus possess similar properties.
₉F = 1s², 2s¹ , 2p⁵
₁₇Cl = 1s², 2s², 2p⁶ , 3s² , 3p⁵
₃₅Br = 1s², 2s², 2p⁶ , 3s², 3p⁶, 3d¹⁰, 4s² , 4p⁵

(i)  Ni = + 2, Pt = + 4
(II) Platinum forms more stable complexes in +4 state due to its higher stability than +2 state.

The energy which is released by an atom in gaining an electron from outside atom or ion to form negative ion (or anion) is called electron gain enthalpy (\(\triangle\)_eg H). Unit of electron gain enthalpy is kJ/mol. In some cases, like in noble gas, atoms do not have any attraction to gain an electron. In that case energy has to be supplied.
For example :
Ne(g) + e^- ⟶ Ne^-(g)
\(\triangle\)_egH = +116 kJ mol^-1

Electronic configuration of A (Z = 12)
1s² 2S² 2p⁶ 3s²
period = 3, Element's name = Mg
block = s, Group = II
Electronic configuration of B (Z = 19)
Element's name K (potassium)
1s² 2S² 2p⁶ 3s² 3p⁶ 4S¹
n = 4, period = 4
Block = s, Group = I
Electronic configuration of C (Z = 29)
1s² 2S² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4S¹
n = 4, period = 4
Block = d
Electronic configuration of D (Z = 36)
1s² 2S² 2p⁶ 3s² 3p⁶ 4S² 3d¹⁰ 4p⁶
period = 4
Block = p-Block
group = 18

(a) All the given species have a same number of electrons  \(({ 10e }^{ 1 })\)Therefore, all are isoelectronic species.
(b) The ionic radii of isoelectronic species decreases with increase in atomic number (as magnitude of the nuclear charge increase with increase in atomic number) 
Therefore, their ionic radii increase in the order.\(\underset { z=13 }{ { Al }^{ 3+ } } <\underset { 12 }{ { Mg }^{ 2+ } } <\underset { 11 }{ { Na }^{ + } } <\underset { 9 }{ { F }^{ - } } <\underset { 8 }{ { O }^{ 2 } } <\underset { 7 }{ { N }^{ 3- } } \)

Electropositive character means tendency to give an electron to form cation. It varies directly with atomic radii. Thus, the correct order is Mg > fe > Cu.

The amount of energy released when 1 x 10¹⁰ atoms of chlorine in vapour state are converted to Cl^- ions, according to the equation.
Cl ( G ) + e^- \(\longrightarrow \) Cl^- ( g ) is 57.86 \(\times \) 10^-10 J
\(\therefore \)  The electron gain enthalpy of ghlorine, i.e. the amount of energy releaed ehen 1 mole ( 6.023 \(\times \) 10²³ ) atoms of chlorineare coverted into Cl^- ions according to the above equation will be
= -\(\frac { 57.86\times { 10 }^{ -10 } }{ 1\times { 10 }^{ 10 } } \times 6.023\times { 10 }^{ 23 }\)
= -348.49 \(\times\) 10³ J mol^-1
= -348.49 kJ mol^-
Now 1 eV/atom = 96.49 kj mol^-1
\(\therefore\)  Electron gain enthalpy of chlorine
= -\(\frac { 348.49 }{ 96.49 }\)
= - 3.61 eV/atom