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

1.	Magnetic quantum number of any element of the period.
2.	Atomic number of any element of the period.
3.	Maximum principal quantum number of any element of the period.
4.	Maximum azimuthal quantum number of any element of the period.

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

The correct order of size of the given species is: 

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

$\mathrm{O}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}\to {\mathrm{O}}^{-}\left(\mathrm{g}\right);<mspace\; width="1em"></mspace>∆{\mathrm{H}}^{⊝}=-141<mspace\; width="1em"></mspace>\mathrm{kJ}<mspace\; width="1em"></mspace>{\mathrm{mol}}^{-1}$
${\mathrm{O}}^{-}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}\to {\mathrm{O}}^2\left(\mathrm{g}\right);<mspace\; width="1em"></mspace>∆{\mathrm{H}}^{⊝}=+780<mspace\; width="1em"></mspace>\mathrm{kJ}<mspace\; width="1em"></mspace>{\mathrm{mol}}^{-1}$

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

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

What is the correct order of elements based on their increasing electron affinity?

Match the elements given in List-I with the atomic radius given in List-II the correct atomic radius with the corresponding element.

Match the correct ionization enthalpies and electron gain enthalpies of the following elements.

Codes