Point mutation may occur due to

The correct option is B change in a single base pair of DNA
Mutations are sudden changes in the structure of genes which include changes in their number or in the arrangement of their nucleotides. Alteration in DNA sequence in chromosomes results in mutations.

Change in a single base pair of DNA causes point mutation. Such a change can be caused either due to replacement of a nucleotide with another one or due to addition or deletion of a single nucleotide pair. Sickle cell anaemia is an example of a disease caused due to point mutation in which there is substitution of a thymine by adenine in the β globin gene.

Deletion or gain of a segment of DNA (one or more nucleotides, not in multiples of three) causes frame-shift mutations. This causes a shift in the frame of the codons and consequently the animo acid sequence in the polypeptide is also changed. The human hereditary disease of muscular dystrophy is caused due to frameshift mutation which leads to weakness in muscles.