s-Block Elements

Nitrogen, sulphur, halogens and phosphorus present in an organic compound are detected by "Lassaigne's test".

$\begin{aligned} & \mathrm{Na}+\mathrm{C}+\mathrm{N} \xrightarrow{\Delta} \mathrm{NaCN} \\ & 2 \mathrm{Na}+\mathrm{S} \xrightarrow{\Delta} \mathrm{Na}_2 \mathrm{~S} \\ & \mathrm{Na}+\mathrm{X} \xrightarrow{\Delta} \underset{(\mathrm{X}=\mathrm{Cl}, \mathrm{Br}, \mathrm{l})}{\mathrm{NaX}} \end{aligned}$

Li, Be forms predominately covalent compounds.

Assertion is correct because all Alkali metals gives deep blue solution by giving electrons.

Reason is incorrect because deep blue solution appears due to the presence of ammoniated electron or solvated electrons.

The daily requirement in the human body has been estimated to be 200-300 mg (NCERT : s-block) Biological importance of magnesium and calcium.

Weight $=2\times16=32$ g

Atomic hydrogen atoms produced by dissociation of dihydrogen with the help of electric arc use for cutting and welding metals with high melting points.

Milk of lime reacts with chlorine to form hypochlorite, a constituent of bleaching powder

2Ca(OH)₂ + 2Cl₂ $\to$ $\mathop {\mathrm{CaC{l_2} + Ca{{(OCl)}_2}}}\limits_{\mathrm{Bleaching\,Powder}} $ + 2H₂O

Calcination involves heating when the volatile matter escapes leaving behind the metal oxide.

Fe₂O₃ . xH₂O(s) $\buildrel \Delta \over \longrightarrow $ Fe₂O₃(s) + xH₂O(g)

ZnCO₃(s) $\to$ ZnO(s) + CO₂(g)

CaCO₃ . MgCO₃(s) $\to$ CaO(s) + MgO(s) + 2CO₂(g)

CaCO₃ + 2HCl $\buildrel \Delta \over \longrightarrow $ CaCl₂ + H₂O + CO₂ Not calcination

It is a neutralization reaction.

$\bullet$ Alkali metals show only '+1' oxidation state in all of their compounds.

KO₂ is a super-oxide in which O$_2^ - $ is anion and K⁺ is cation oxidation state of K is +1.

$\bullet$ Cs is used in photoelectric cell due to its low ionisation enthalpy

$\bullet$ KOH used to absorb CO₂ and changes into K₂CO₃

$\bullet$ Liquid sodium metal is used as a coolant in fast breeder nuclear reactor

$\bullet$ Lithium is used in electrochemical cells

Solubility of fluorides of alkaline earth metals decreases down the group due to more increase in value of lattice enthalpies as compared to hydration-enthalpy.

Thus, the order of solubility of given compounds is as follows :

$\mathrm{BeF}_2>\mathrm{MgF}_2>\mathrm{CaF}_2>\mathrm{SrF}_2$

Hence, $\mathrm{BeF}_2$ has maximum solubility.

Both assertion and reason are correct and reason is the correct explanation of the assertion. $\mathrm{BeO}$ is more stable than $\mathrm{BeCO}_3$ due to small size and high polarising power of $\mathrm{Be}^{2+}$.

As $\mathrm{BeCO}_3$ is unstable and $\mathrm{BeO}$ is more stable thus, when $\mathrm{BeCO}_3$ is kept in an atmosphere of $\mathrm{CO}_2$, a reversible process takes place and stability of $\mathrm{BeCO}_3$ increases. The reaction is shown below

$\mathrm{BeCO}_3 \rightleftharpoons \mathrm{BeO}+\mathrm{CO}_2$