# Poly$- \beta -$hydroxybutyrate-co$- \beta -$hydroxy valerate (PHBV) is a copolymer of:A. $3 -$hydroxybutanoic acid and $4 -$hydroxypentanoic acidB. $2 -$ hydroxybutanoic acid and $3 -$hydroxypentanoic acidC. $3 -$ hydroxybutanoic acid and $2 -$hydroxypentanoic acidD. $3 -$ hydroxybutanoic acid and $3 -$hydroxypentanoic acid

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Hint: Polymer is a substance or material made up of very large molecules or macromolecules made up of numerous repeating subunits. Natural and manmade polymers both play important parts in our daily lives due to their broad spectrum. Polymers are crucial to biological structure and function, ranging from synthetic plastics such as polystyrene to natural polymers and natural biopolymers such as protein and DNA.

Complete Step by Step Solution:
PHBV stands for Poly$- \beta -$hydroxybutyrate-co$- \beta -$hydroxyvalerate. It is a polyhydroxyalkanoate polymer of some sort. It is a non-toxic natural biodegradable plastic made by bacteria that can be utilised as an alternative to synthetic polymers.
The structure of PHBV is as follows:

Image: Structure of PHBV
Two (or more) types of monomer units are used to make a copolymer. Two (or more) types of monomer units can be found in the copolymer's repeating structural unit.
PHBV is prepared by the reaction as follows:

Image: Reaction to prepare PHBV
Therefore, PHBV is a copolymer of $3 -$ hydroxybutanoic acid and $3 -$hydroxypentanoic acid.

Additional Information: Many bacteria, such as Paracoccus denitrificans, generate it naturally, and many genetically altered plants can also produce it. PHBV is a brittle thermoplastic polymer with poor elongation at break and limited impact resistance.

Note: Because of the geometry of the f-orbitals, the elements near the bottom of the group have f-subshell electrons that are diffused. They successfully shelter the s-electrons from the nucleus's attraction and render them bonding inactive.