Correct Answer: To confer certain unique phenotypic characters to bacteria.

Solution : The correct option is to confer certain unique phenotypic characteristics to bacteria .

Plasmid DNA functions to confer unique phenotypic traits to bacteria. It carries non-essential genetic information, such as antibiotic resistance genes or the ability to metabolise specific compounds. These traits provide a selective advantage to bacteria in different environments and can be passed on through horizontal gene transfer, enhancing bacterial adaptability and survival.