Plasmid is a
a. Single-stranded DNA.
b. Double-stranded circular DNA.
c. Extrachromosomal linear DNA.
d. RNA.

Hint: Plasmids are called replicons. It is found mainly in a bacterial cell but it can also be located in some eukaryotes. The plasmid can be made artificially which is used in molecular cloning as the vector. The plasmids which are found in viruses are not considered as life. In some cases, plasmids are found in linear shape and comprise RNA as the genetic material.

Complete answer:
> Option A: Single stranded DNA (ssDNA) comprises a single DNA as the genetic material. Thus it is called ssDNA. It is found in some viruses like Mono Avira sp. Some bacteriophages like M-13 also carry out single stranded DNA.

> Option B: A plasmid is a double stranded circular DNA. Plasmid generally carries out those genes that produce selective advantages (like antibiotic resistance) to the bacteria.

> Option C: Extrachromosomal linear DNA is found in many prokaryotic organisms like Borrelia sp. Extrachromosomal DNA is found outside the nucleoid region of the prokaryotic cell.

> Option D: Ribonucleic acid is an essential biomolecule that plays a major role in many biochemical reactions (regulation and expression of genes, coding) of the body. A plasmid is not an RNA molecule. RNA is composed of nucleotides. Nucleotides comprise nitrogenous base, sugar, and a phosphate group. Nitrogenous bases are two types, named purine and pyrimidine. Purine involves adenine and guanine and pyrimidine involves cytosine and uracil. RNA comprises a single strand.

Hence, the correct answer is option (B).

Note: Plasmid consists of genes which encode plasmid specific replication initiation protein, iterons, AT-rich regions, Dna boxes. A plasmid is capable of replicating independently. There are two types of plasmids found, named conjugative plasmid and non-conjugative plasmid.