Haloalkanes of the form$\mathrm{R}-\mathrm{Br}$ and $\mathrm{R}-\mathrm{I}$develop colour when exposed to light.

• As we progress down the periodic table from fluorine to iodine, molecular size increases.
• As a result, we also see an increase in bond length.
• As the bond length increases, upon irradiation of light, after absorption the compound emit light in visible region.
• Therefore, $\mathrm{R}-\mathrm{Br}$ and $\mathrm{R}-\mathrm{I}$ bond exhibit color when exposed to light.

$\begin{array}{cccccc}{X}^{19}& :& 1s^2& 2s^{2}2p^6& 3s^{2}3p^6& 4s^1\\ & & K& L& M& N\\ Y^{21}& :& 1s^2& 2s^{2}2p^6& 3s^{2}3p^{6}3d^1& 4s^1\\ & & K& L& M& N\\ Z^{25}& :& 1s^2& 2s^{2}2p^6& 3s^{2}3p^{6}3d^5& 4s^1\\ & & K& L& M& N\end{array}$

Electrons in $M$ shell of these elements are

$Z^{25}(13)>Y^{21}(9)>X^{19}(8)$

Crystalline solids are anisotropic in nature.

• It is because the arrangement of constituent particles is regular and ordered along all the directions.
• Therefore, the value of any physical property (electrical resistance or refractive index) would be different along each direction.
  
• That is, some of their physical index show different values when measured along different directions in the same crystal.
  

A pressure cookeris a closed system.

There will be no interactions with the surroundings. For example, the contents of a pressure cooker on a stove with its lid tightly closed and the whistle in position is a closed system as no mass can enter or leave the pressure cooker, but heat can be transferred to it.

Given that:

The iron oxide has $69.9\mathrm{\%}$ iron and $30.1\mathrm{\%}$ dioxygen by mass.

Thus, $100\mathrm{g}$ of iron oxide contains $69.9\mathrm{g}$ iron and $30.1\mathrm{g}$ dioxygen.

The number of moles of iron present in $100\mathrm{g}$ of iron oxide are:

$=\frac{\text{ Mass }}{\text{ Atomic mass }}$

$=\frac{69.9}{55.8}$

$=1.25$

The number of moles of dioxygen present in $100\mathrm{g}$ of iron oxide are:

$=\frac{\text{ Mass }}{\text{ Atomic mass }}$

$=\frac{30.1}{32}$

$=0.94$

The ratio of the number of oxygen atoms to the number of iron atoms present in one formula unit of iron oxide is:

$=\frac{2\times 0.94}{1.25}$

$=1.5:1$

$=3:2$

Therefore, the formula of the iron oxide is ${\mathrm{Fe}}_2{\mathrm{O}}_3$.

Number of donor atoms in $N{\left(C{H}_{2}C{H}_{2}N{H}_2\right)}_3$ is four so it is a tetradentate ligand. Each nitrogen atom is a donor atom.

The compound which can be easily dehydrated will form most stable carbocation after removal of ${\mathrm{H}}_2\mathrm{O}$ molecule.

Since stability of carbocation follows 3 degree> 2 degree> 1 degree

So, compound $A$ is most easily dehydrated.

Across the lanthanide series the size of the cations decreases thereby decreasing ionic character and increasing covalent character of hydroxides of lanthanides. Thus, the basicity of hydroxides decreases.