Question

The correct statement from (a) to (d) are:
a.) Saline hydrides produce ${{H}_{2}}$ gas when reacting with ${{H}_{2}}O$.
b.) Reaction of $LiAl{{H}_{4}}$ with $B{{F}_{3}}$ leads to ${{B}_{2}}{{H}_{6}}$
c.) $P{{H}_{3}}$ and $C{{H}_{4}}$ are electron-rich and electron-precise hydrides, respectively.
d.) HF and $C{{H}_{4}}$ are called molecular hydrides.

A.) (c) and (d) only
B.) (a), (b) and (c) only
C.) (a), (b), (c) and (d)
D.) (a), (c) and (d) only

Answer 1

. To solve this type of question it is important that we have prior knowledge about the reactions involved. Lithium aluminium hydride is a reducing agent which can reduce aldehydes to primary alcohols, ketones to secondary alcohols etc.

Complete step by step answer:
Let’s check whether the given statements are correct or incorrect.
Saline hydrides produce ${{H}_{2}}$ gas when reacts with ${{H}_{2}}O$ : this statement is a true statement, saline hydride or ionic hydride when combines with water it forms metal hydroxide and evolution of hydrogen gas takes place. The reaction involved is mentioned below:
$MH+HOH\to MOH+{{H}_{2}}$

Reaction of $LiAl{{H}_{4}}$ with $B{{F}_{3}}$ leads to ${{B}_{2}}{{H}_{6}}$: this statement is also true, $B{{F}_{3}}$ reacts with lithium aluminium hydride and produce diborane along with lithium fluoride and aluminium fluoride. The reaction involved is shown below:
$4B{{F}_{3}}+3LiAl{{H}_{4}}\to 2{{B}_{2}}{{H}_{6}}+3LiF+3Al{{F}_{3}}$

$P{{H}_{3}}$ and $C{{H}_{4}}$ are electron-rich and electron-precise hydrides, respectively: this statement is also correct as phosphorus has 5 electrons in the valence shell and after combining with hydrogen it becomes an electron rich molecule having more than 8 electrons in its outermost shell similarly carbon has 4 electrons in its outermost shell and after combining with 4 hydrogen atoms it becomes an electron precise molecules having a complete octet.
HF and $C{{H}_{4}}$ are called molecular hydrides: This statement is also correct because both hydrogen fluoride and methane are covalent molecules.
So, the correct answer is “Option C”.

Note: To determine whether the molecule is electron deficient or not we should determine that the atoms in molecule have their complete octet i.e. eight electrons in the outermost shell or duplet i.e. 2 electrons in the outermost shell. Duplet is only applicable in some of the atoms.