Question

Which of the following facts regarding boron and silicon is true?
(A) Boron and silicon are semiconductors.
(B) Boron and silicon form halides which are hydrolysed.
(C) Boron and silicon react with magnesium to form magnesium boride and magnesium silicide which are decomposed by acids to give volatile borane and silane, respectively.
(D) Both boron and silicon react with alkalis to form borates and silicates containing $B{{O}_{4}}$ and $Si{{O}_{4}}$ tetrahedral units, respectively.

Answer 1

To solve this question we first need to know what are boron and silicon.
The chemical element with atomic number 5 is boron and it occurs naturally as borate minerals which are soluble in water.
The chemical element with atomic number 14 is silicon and even though it does not occur naturally as a pure element, it is the 8th most common element by mass.

Complete answer:
(A) The statement that boron and silicon are semiconductors is false.
(B) The statement that boron and silicon form halides which are hydrolyzed is true.
The halide form by boron is boron trichloride ($BC{{l}_{3}}$) and the halide formed by silicon is silicon tetrachloride ($SiC{{l}_{4}}$).
The hydrolysis reaction of boron trichloride ($BC{{l}_{3}}$) is as follows
$BC{{l}_{3}}+3{{H}_{2}}O\to B{{(OH)}_{3}}+3HCl$
The hydrolysis reaction of silicon tetrachloride ($SiC{{l}_{4}}$) is as follows
$SiC{{l}_{4}}+{{H}_{2}}O\to Si{{(OH)}_{4}}+4HCl$
Both these chlorides are liquids, they are easily hydrolyzed by water and fuming in the air.
(C) The statement that boron reacts with magnesium to form magnesium boride which is decomposed by acids to give volatile borane and silicon reacts with magnesium to form magnesium silicide which is decomposed by acids to give volatile silane is false.
(D) The statement that boron reacts with alkalis to form borates containing $B{{O}_{4}}$ tetrahedral units and silicon reacts with alkalis to form silicates containing $Si{{O}_{4}}$ tetrahedral units is false.

So, the correct answer is option (B).

Note:
It should be noted that silicon is a semiconductor but boron is not a semiconductor. Boron instead is used as a dopant in semiconductors. A dopant is an impurity that is introduced in an intrinsic semiconductor on purpose. Boron is a p-type dopant.