Question

The following are the two reaction schemes involving Mg.
Scheme 1:$\begin{align}
& Mg\xrightarrow{air}colourless\,solid\,A\xrightarrow{HCl}colourless\,solution\,B\xrightarrow{N{{a}_{2}}C{{O}_{3}}}white\,ppt\,C \\
 & \xrightarrow{\Delta }D\,colourless\,gas\,E\xrightarrow{Ca{{(OH)}_{2}}}white\,ppt\,F \\
\end{align}$

Scheme 2:$\begin{align}
 & Mg\xrightarrow{dil\,{{H}_{2}}S{{O}_{4}}}colourless\,solution\,G\xrightarrow{NaOH}white\,ppt\,H\xrightarrow{HN{{O}_{3}}}colourless\, \\
 & solution\xrightarrow{evaporate}I\xrightarrow{\Delta }J\,gas+{{O}_{2}}+D \\
\end{align}$
Find I.
A.$Mg(N{{O}_{2}})$
B.$Mg{{(N{{O}_{2}})}_{2}}$
C.$Mg{{(N{{O}_{3}})}_{2}}$
D.$Mg(N{{O}_{3}})$

Answer 1

Hint: The physical as well as the chemical properties of Magnesium need to be known for answering this question. Magnesium falls in the alkaline earth metals of the S block and has the electronic configuration of $[Ne]3{{s}^{2}}$.

Complete answer:
In order to answer our question, we need to learn about the Alkaline Earth metals of the s block. The alkaline earth metals are silvery white, lustrous and relatively soft but harder than the alkali metals.
Beryllium and magnesium appear to be somewhat greyish. The boiling and melting points of these metals are higher than the corresponding alkali metals as they have small atomic size. But because of the low ionisation enthalpies, this trend is not systematic, in fact they are strongly electropositive in nature. The electropositive character increases from Be to Ba down the group.

Barium, strontium and calcium show characteristic apple green, crimson and brick red colours to the flame respectively. In flame due to the heat and wavelength, the electrons are pushed to higher energy levels and when they return to the ground state, energy gets released as visible light. However the electrons in magnesium and beryllium cannot get excited due to good bonding. So, no colour is shown by these elements in the flame. Sr, Ca and Ba give flame tests which show their detection in estimation by flame photometry and qualitative analysis. The alkaline earth metals behave like those of alkali metals have high electrical and thermal conductivities which are a typical characteristics of metals.

Now, let us come to a solution. Mg when heated in air gives us white solid MgO and when It reacts with HCl,$MgC{{l}_{2}}$ is produced. This on reaction with $N{{a}_{2}}C{{O}_{3}}$ gives us $MgC{{O}_{3}}$ and on heating gives MgO and $C{{O}_{2}}$. $Ca{{(OH)}_{2}}$ reacts with it to form $CaC{{O}_{3}}$.
\[Mg\xrightarrow{air}MgO\xrightarrow{HCl}MgC{{l}_{2}}\xrightarrow{N{{a}_{2}}C{{O}_{3}}}MgC{{O}_{3}}\xrightarrow{\Delta }MgO+C{{O}_{2}}\xrightarrow{Ca{{(OH)}_{2}}}CaC{{O}_{3}}\]
The scheme 2 can be represented as:
\[Mg\xrightarrow{dil\,{{H}_{2}}S{{O}_{4}}}MgS{{O}_{4}}\xrightarrow{NaOH}Mg{{(OH)}_{2}}\xrightarrow{HN{{O}_{3}},evaporate}Mg{{(N{{O}_{3}})}_{2}}\xrightarrow{\Delta }N{{O}_{2}}+{{O}_{2}}+MgO\]

As we can see from the scheme that the required compound is $Mg{{(N{{O}_{3}})}_{2}}$. So, we obtain our answer as option C.

Note:
It is to be noted that salts of magnesium occur in sea water. Magnesium has a closed packed hexagonal lattice. Magnesium ion is the essential element in the human body and the important constituent of chlorophyll.