The S-Block Elements

\(
\begin{aligned}
&\begin{array}{cc}
\text { Element } & \text { Density }\left( g m / c m ^3\right) \\
Be & 1.84 \\
Mg & 1.74 \\
Ca & 1.55 \\
Sr & 2.63
\end{array}\\
&Ca \text { has least density among the given elements. }
\end{aligned}
\)

The element with the smallest size among Li, Na, K, Be, B, Mg is Boron (B).

Boron forms B₂O₃ which corresponds to the A₂​O_3​ type of oxide.

Correct answer: Option A

Smaller the size of anion, smaller is the covalent character and higher will be its melting point. Hence, the order of melting point of lithium salts is LiF > LiCl > LiBr.

For a given metal \(\Delta_{ f } H ^0\) always becomes less negative from fluoride to iodide. Therefore correct order of standard enthalpy of formation of \(NaX\) is \(Na I < NaBr\) \(< NaCl < NaF\)

\(Na > Cs > Li -\) true \(\{\) If considered with sign \(\}\)

CsI is less soluble in water due to smaller hydration enthalpy of it's two ions
\(Li _2 CO _3\) is not so stable to heat and gets converted into \(Li _2 O\) and \(CO _2\).
Potassium dissolved in liquid ammonia give deep blue solutions that are paramagnetic but in the concentrated solution, the blue. All the alkali metal hydrides are ionic solid (True).

Smaller the size of anion, smaller is the covalent character and higher will be its melting point. Hence, the order of melting point of lithium salts is LiF > LiCl > LiBr.

The element with the smallest size among Li, Na, K, Be, B, Mg is Boron (B).

Boron forms B₂O₃ which corresponds to the A₂​O_3​ type of oxide.

Correct answer: Option A

The best method for the preparation of \(BeF _2\) in the given methods is heating of \(\left( NH _4\right)_2 BeF _4\)
It is given as,
\[
\left( NH _4\right)_2 BeF _4 \xrightarrow{\Delta} BeF _2+ NH _4 F
\]