Among halogens, the correct order of amount of energy released in electron gain (electron gain enthalpy) is-

1.	F > Cl > Br > I	2.	F < Cl < Br < I
3.	F < Cl > Br > I	4.	F < Cl < Br > I

The period number in the long form of the periodic table is equal to : 

The elements in which electrons are progressively filled in 4f-orbitals are called:

The correct order of size of the given species is: 

1.  I > I^- > I⁺

2.  I⁺ > I^- > I

3.  I > I⁺ > I^-

4.  I^- > I > I⁺

The formation of oxide ion O^2-(g), from oxygen atom, requires first an exothermic and then an endothermic step as shown below

$\mathrm{O}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}\to {\mathrm{O}}^{-}\left(\mathrm{g}\right); ∆{\mathrm{H}}^{⊝}=-141 \mathrm{kJ} {\mathrm{mol}}^{-1}$
${\mathrm{O}}^{-}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}\to {\mathrm{O}}^2\left(\mathrm{g}\right); ∆{\mathrm{H}}^{⊝}=+780 \mathrm{kJ} {\mathrm{mol}}^{-1}$

Thus, the process of formation of O^2- in the gas phase is unfavourable even though O^2- is isoelectronic with neon. It is due to the fact that

The outermost electronic configuration of the last element of the p-block in the 6th period is represented by:

1. $7{\mathrm{s}}^{2}7{\mathrm{p}}^6$

2. $5{\mathrm{f}}^{14}6{\mathrm{d}}^{10}7{\mathrm{s}}^{2}7{\mathrm{p}}^0$

3. $4{\mathrm{f}}^{14}5{\mathrm{d}}^{10}6{\mathrm{s}}^{2}6{\mathrm{p}}^6$

4. $4{\mathrm{f}}^{14}5{\mathrm{d}}^{10}6{\mathrm{s}}^{2}6{\mathrm{p}}^4$

Among the following elements whose atomic numbers are given below, which cannot be accommodated in the present set up of the long periodic table?

The elements with atomic numbers 35, 53, and 85 are:

Electronic configuration of four elements A, B, C and D are given below : 

A. $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^6$

B. $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^4$

C. $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^1$

D. $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^5$

The correct order of increasing tendency to gain electron is : 

Match the correct atomic radius with the corresponding element.

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