\[C{O_2}\] is a gas, while \[Si{O_2}\] is a solid but both are:
(A) Covalent containing \[\pi \]-bond
(B) Molecules having \[p\pi - d\pi \] bonding
(C) Acidic
(D) Discrete molecules

Hint: Carbon dioxide is a colourless gas with a density about 60% higher than that of dry air. Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms. It occurs naturally in Earth's atmosphere as a trace gas.
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula \[Si{O_2}\], most commonly found in nature as quartz and in various living organisms.

Complete step by step answer:
> To solve this question we need to consider the following characteristics of \[C{O_2}\] and \[Si{O_2}\].
> In \[C{O_2}\] (displayed formula: O=C=O), each molecule is attracted to other molecules because of what is called “van der Waals forces” or London forces.
- Van der Waals forces are a very weak form of intermolecular force where temporary and induced dipoles attract one another.
- Van der Waals forces can be broken with little energy, thus carbon dioxide melts at just over -56.6 degrees Celsius.
> In \[Si{O_2}\], every silicon atom is bonded (covalent) to four oxygen atoms. Every oxygen atom is bonded to two silicon atoms.
This forms a giant, tetrahedral structure much like a diamond. All the atoms are interconnected by covalent bonds, making the lattice incredibly strong.
This is proven by the fact that \[Si{O_2}\] has a melting point of 1713 degrees Celsius (Iron melts at 1538 degrees Celsius).
So the answer is option D discrete molecules.

Note: \[C{O_2}\] consists of individual molecules with one central carbon atom double bonded to two oxygen atoms. Whereas, Silicon does not form double bonds with oxygen. \[C{O_2}\] is gas but \[Si{O_2}\] is solid because the \[Si{O_2}\] is in giant molecular structure but the \[C{O_2}\] is simple molecular structure. Because of this reason \[C{O_2}\] is gas but \[Si{O_2}\] is solid.