Point mutation involves-
a. Deletion
b. Insertion
c. Change at single base pair
d. All of the above

Hint: Point mutations are a broad group of mutations that define a difference in the nucleotide location of the long double helix DNA strand causing the DNA to differ from the typical or wild gene.

Complete answer:
> Option A is incorrect. A deletion mutation is an error in the process of DNA replication which removes nucleotides from the genome. A deletion mutation can delete a single nucleotide or whole nucleotide sequences.

> Option B is incorrect. Adding one or more nucleotide base pairs to a DNA sequence is an insertion. Because of the slipping of DNA polymerase, this may also happen in microsatellite regions.

> Option C is incorrect. A point mutation is a mutation involving only a single nucleotide nucleic acid. Most generally, point mutations include the substitution of one base for another (which often affects the complimentary basis in DNA).

> Option D is correct. A point mutation defines a shift in a single DNA nucleotide so that the nucleotide is transferred to another nucleotide, or the nucleotide is removed, or a new nucleotide is added into the DNA.
So, the correct answer is Option D.

Additional information:
The mutation of a fragment of DNA in a single nucleotide base is called a point mutation. It happens by mutation substitution or frameshift. The exchange of one nitrogen base is called substitution for another. The transformation is to substitute one type of base with another of its kind (purine -purine and pyrimidine -pyrimidine). Replacement of purine base for a pyrimidine base or pyrimidine base replacement to a purine base is called transversion. The gene mutations that change the base sequence of the entire genetic structure from the mutation point onwards are called frameshift mutations. Here the base sequence read frame is pushed forward (due to addition of one or more nucleotide base) or backward (due to deletion of one or more nucleotide base). Duplication is the presence of an extrachromosomal segment attached to the normal homologous chromosome which causes duplication of a set of genes in the same chromosome; therefore, it is not a point mutation.

Note: Point mutation modifications within a gene where one base pair is altered in the DNA sequence. Point mutations are often the result of mistakes made during DNA replication, while alteration of DNA can also cause point mutations, such as exposure to X-rays or ultraviolet radiation.