Steel pipes running through industrial plants are exposed to a punishing combination of conditions: mechanical vibration from pumps and flow, cyclic thermal expansion and contraction, and contact with corrosive chemicals such as acids, alkalis and solvents. A protective coating is chosen for its ability to survive all of these while keeping an unbroken barrier over the steel, because any crack or breach lets moisture and chemicals reach the metal and start corrosion.

Why the flexibility and chemical resistance answer is correct: Rubber-based coatings are elastomeric — they stretch and flex elastically, so when the pipe vibrates or expands and contracts the coating deforms with it instead of cracking, keeping the seal intact. Rubber is also chemically inert to many acids, bases and solvents, so it resists chemical attack. This pairing of mechanical flexibility and chemical resistance is exactly what makes rubber coatings well suited to protecting pipes in these environments.

Why the other options are wrong:

• Improving electrical conductivity is not a purpose of the coating; rubber is in fact an electrical insulator, and a protective barrier coating is not applied to make the surface conduct.
• Providing high thermal conductivity is likewise not the goal; rubber is a relatively poor conductor of heat, and protection does not depend on conducting heat well.
• Colour durability under sunlight is at best a minor cosmetic benefit and irrelevant to indoor or buried industrial pipework; it does nothing to address vibration or chemical attack, which are the real threats.

Hence the key property is the coating's flexibility that prevents cracking under vibration together with its resistance to chemical attack.