Question

Assertion: $ PC{l_5} $ Is an unstable molecule.
Reason: Formation of $ PC{l_5} $ does not follow octet rule.
(A) Both assertion and reason are correct statements, and reason is the correct explanation of the assertion
(B)Both assertion and reason are correct statements, but reason is not the correct explanation for assertion
(C)Assertion is correct, but reason is wrong statement
(D)Both Assertion and Reason are false statement ​

Answer 1

Hint :The chemical compound $ PC{l_5} $ stands for phosphorus pentachloride. One of the most significant phosphorus chlorides, along with $ PC{l_3} $ and $ POC{l_3} $ . As a chlorinating reagent, $ PC{l_5} $ is used. Although commercial samples can be yellowish and polluted with hydrogen chloride, it is a colourless, water-sensitive, and moisture-sensitive solid.

Complete Step By Step Answer:
The phosphorus chlorides' structures are always compatible with VSEPR theory. $ PC{l_5} $ 's structure is influenced by its surroundings. $ PC{l_5} $ is a neutral molecule with trigonal bipyramidal geometry and ( $ {D_3}h $ ) symmetry that is gaseous and molten. The existence of non-bonding molecular orbitals (molecular orbital theory) or resonance can explain the hypervalent character of this species (valence bond theory). $ PC{l_5} $ is an ionic chemical in its solid state.
There are equatorial bonds in $ PC{l_5} $ , in addition to axial bonds that are in the same plane. Axial bonds are longer than conventional bonds because electrons in them experience higher repulsion. As a result, axial bonds in $ PC{l_5} $ are longer than equatorial ones. As a result, these axial linkages are weak bonds that may readily be broken. $ PC{l_5} $ Is unstable for these reasons, and hence quickly dissociates to produce $ PC{l_3} $ .
 $ PC{l_5} $ is $ s{p^3}{d^2} $ hybridised and has a trigonal bipyramidal structure with three cations at the equatorial position and two at the axial position. It takes on this form in order to reduce interelectronic repulsion between a-atoms. Phosphorus has 5 -electrons in its valence shell, allowing it to form five covalent bonds.
Hence option C is correct.

Note :
The octet rule is a chemical rule of thumb that represents the hypothesis that main-group elements tend to bind in such a way that each atom has eight electrons in its valence shell, resulting in an electronic configuration similar to that of a noble gas. The law applies to carbon, nitrogen, oxygen, and halogens in particular, but also to metals like sodium and magnesium. A Lewis electron dot diagram, as illustrated to the right for carbon dioxide, can be used to count the valence electrons. In a covalent link, the electrons shared by the two atoms are tallied twice, one for each atom.