Question

Assertion
Statement 1: Silicon exists only in diamond-like structure while carbon exists both in diamond and graphite forms.
Reason
Statement 2: Carbon can show pronounced $p\pi - p\pi $ bonding while silicon shows negligible extent of $p\pi - p\pi $ bonding.
A.Statement 1 is True, Statement 2 is True; statement 2 is a correct explanation for statement 1.
B.Statement 1 is True, statement 2 is True; statement 2 is not a correct explanation for statement 1.
C.Statement 1 is True, statement 2 is False.
D.Statement 1 is False, statement 2 is True.

Answer 1

Hint: Diamond and Graphite are the allotropes of carbon. Some elements exhibit the property named as allotropy, in this the elements exist in two or more forms in the same physical state and the forms attained are termed as allotropes of the elements. Catenation is the property exhibited by the elements that is to form covalent bonds with itself. Carbon shows catenation while silicon shows less catenation.

Complete step by step answer:
Graphite is a macromolecule that is made up of hexagonal carbon rings. The carbons have $s{p^2}$ hybridization and form 2 sigma bonds and one pi bond (pronounced $p\pi - p\pi $ bonding) each. Silicon, being in the same group does have similarities but it does not form macromolecules only with itself like the carbon. This due to the catenation property of the elements.
Carbon has the highest tendency to form covalent bonds due to which it has the highest catenation tendency. Due to this property, we could see long chains of carbon.
Silicon having lesser catenation property than carbon is due to their respective bond energies. A $C - C$ bond is very strong, providing high stability to the molecule whereas a $Si - Si$ bond is not so strong. That is why silicon cannot form macromolecules with itself like carbon. Silicon because of its larger size shows a negligible tendency to form $\pi - \pi $ bonding due to which it exists only in diamond-like form whereas carbon exists in both diamond and graphite forms.
Therefore, statement 2 is the correct explanation for statement 1.
Hence, the correct option is (A).

Note:
Carbon and silicon belong to group 15 elements.
The atomic number of carbon is 6 and its electronic configuration is $1{s^2}2{s^2}2{p^2}$.
The atomic number of silicon is 14 and its electronic configuration is $1{s^2}2{s^2}2{p^6}3{s^2}3{p^2}$
Carbon is metal whereas silicon is a metalloid and there are 4 electrons in the outermost orbital of both the atoms.