Question

Assertion: Both boron and silicon form binary compounds with several metals to give borides and silicide.
Reason: These borides and silicides react with ${H_3}P{O_4}$ to give a mixture of boranes and silanes.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C. Assertion is correct but reason is incorrect.
D. Both Assertion and Reason are incorrect.

Answer 1

A boride is a compound between boron and a less electronegative element, for example silicon boride ($Si{B_3}$ and $Si{B_6}$ ). A silicide is a compound that has silicon with (usually) more electropositive elements. Silicon is more electropositive than carbon.

Complete answer:
The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. Some borides exhibit very useful physical properties. The term boride is also loosely applied to compounds such as ${B_{12}}A{s_2}$ (Arsenic has an electronegativity higher than boron) that is often referred to as icosahedral boride.
Similar to borides and carbides, the composition of silicides cannot be easily specified as covalent molecules. The chemical bonds in silicides range from conductive metal-like structures to covalent or ionic. Silicides of all non-transition metals, with exception of beryllium, have been described. Silicides react with a variety of electropositive elements to give several binary chains or ring-like structures.
Thus, both boron and silicon form binary compounds with several metals to give borides and silicide.
On reaction with borides and silicides, phosphoric acid gives a mixture of boranes and silanes. The reaction can be demonstrated with the given chemical equation:
$2C{a_3}{B_2} + 4{H_3}P{O_4} \to {B_4}{H_{10}} + 2M{g_3}{(P{O_4})_2} + {H_2}$
$3M{g_2}Si + 4{H_3}P{O_4} \to 3Si{H_4} + 2M{g_3}{(P{O_4})_2}$
But the reason does not explain the assertion although both the statements are true.

Thus, the correct option is B.

Note:
Borane is the name given to the class of synthetic hydrides of boron with generic formula ${B_x}{H_y}$ . It is a group 13 hydride. Silane is an inorganic compound with chemical formula, $Si{H_4}$ , making it a group 14 hydride. It is a colourless, pyrophoric, toxic gas with a sharp, repulsive smell, somewhat similar to that of acetic acid.