Periodicity of Physical Properties

The ions  ${\mathrm{O}}^{2-},{\mathrm{F}}^{-},{\mathrm{Na}}^{+},{\mathrm{Mg}}^{2+}\mathrm{and}{\mathrm{Al}}^{3+}$ are isoelectronic. Their ionic radii show:

Why does elements of Group$14$ have high melting points and what is the variation of melting point down the group?

Explain why metals have high melting points.

The electrical conductivity increases down the group in the periodic table.

Discuss the trend of electrical conductivity down the group in a periodic table.

The correct order of energy of $2\mathrm{s}$-orbitals in $\mathrm{H}$, $\mathrm{Li}$, $\mathrm{Na}$ and $\mathrm{K}$, is
 

Nuclear charge increases with an increase in ________.

Effective nuclear charge on $\mathrm{N}$-atom and ${\mathrm{N}}^{-}$ ion is:

The shielding constant for $ \mathrm{Zn}$ is:

Which of the following has the highest melting point?

Which of the following pairs show reverse properties on moving along a period from left to right and from top to down in a group?

The metal having highest melting point is?

The melting points of the following halides follow the order

In which case is the effective nuclear charge minimum?

Shielding constant σ for Ne is 4.15. The effective nuclear charge on Na⁺ and F^– are respectively :

Amongst the halogens ${\mathrm{F}}_2, {\mathrm{Cl}}_2, {\mathrm{Br}}_2, {\mathrm{I}}_2$ the correct arrangement on the basis of increasing melting point is