Question

Among the following the correct statements are
I. LiH, BeH\( _2 \) and MgH\( _2 \) are saline hydrides with significant covalent character
II. Saline hydrides are volatile
III. Electron - precise hydrides are Lewis bases
IV. The formula for chromium hydride is CrH The correct option is

• A. I, III only
• B. II, IV only
• C. I, IV only
• D. III, IV only

Hint:

Classify hydrides into saline (ionic), metallic (interstitial), and covalent (molecular) types. Understand the properties associated with each type, such as volatility and Lewis acid-base behavior. Be aware of the exceptions and the factors influencing the nature of bonding in hydrides, like electronegativity and polarizing power. For transition metal hydrides, remember their non-stoichiometric nature.

Answer 1

The Correct Option is C

Let's analyze each statement: I.
**LiH, BeH\( _2 \) and MgH\( _2 \) are saline hydrides with significant covalent character.
** Saline hydrides are typically formed by alkali and alkaline earth metals with hydrogen.
They are generally ionic in nature.
However, the electronegativity difference between the metal and hydrogen decreases down Group 2.
BeH\( _2 \) and MgH\( _2 \) exhibit significant covalent character due to the small size and relatively higher polarizing power of Be\( ^{2+} \) and Mg\( ^{2+} \) ions compared to other heavier alkaline earth metals.
LiH, although primarily ionic, also shows some covalent character due to the relatively small size and higher polarizing power of Li\( ^{+} \).
Thus, this statement is correct.
II.
**Saline hydrides are volatile.
** Saline hydrides are ionic solids with high melting and boiling points.
Due to the strong electrostatic forces between the metal cations and hydride anions, they are non-volatile.
This statement is incorrect.
III.
**Electron - precise hydrides are Lewis bases.
** Electron-precise hydrides are formed by elements of Group 14 (e.
g.
, CH\( _4 \), SiH\( _4 \), GeH\( _4 \)).
The central atom in these hydrides has exactly the number of electrons required to form covalent bonds with hydrogen, without any lone pairs.
Therefore, they are generally electron deficient and do not act as Lewis bases (electron pair donors).
They are typically non-polar or weakly polar and do not have a tendency to donate electron pairs.
This statement is incorrect.
IV.
**The formula for chromium hydride is CrH.
** Transition metals form metallic or interstitial hydrides, which are typically non-stoichiometric.
Chromium forms a non-stoichiometric hydride, often represented as CrH\( _x \), where \( x \) is not a fixed integer.
However, the simplest formula is sometimes represented as CrH, indicating the presence of hydrogen in the metal lattice.
Given the options, considering the possibility of a simplified representation, this statement can be considered plausible in the context of basic formulas, although the stoichiometry is not precise.
Considering the options, statement I is definitely correct.
Statement IV is plausible as a simplified representation of chromium hydride.
Statements II and III are incorrect.
Therefore, the option containing I and IV is the most likely correct answer.
Final Answer: The final answer is $\boxed{I, IV only}$