Final answer:
An individual of a species with 2n = 28 chromosomes having 42 chromosomes is triploid, meaning they have three copies of each chromosome.
Step-by-step explanation:
A species that has 2n = 28 chromosomes means that its diploid number (the total number of chromosomes in a somatic cell) is 28. Hence, each set of chromosomes (n) would be 14. If an individual of this species has 42 chromosomes, they have three complete sets, since 42 divided by 14 equals 3. This means the individual is triploid, having three copies of each chromosome instead of the usual two (diploid).
During the production of gametes in meiosis, errors can sometimes occur that lead to gametes with an incorrect number of chromosomes. If such gametes are involved in fertilization, the offspring may have a chromosome number that is not typical for the species (euploid individuals have the typical number). An extra set of chromosomes, as in the case of the individual with 42 chromosomes, is a form of aneuploidy specific to polyploidy, where there are more than two sets of chromosomes. The options provided in the question (tetraploid, monosomic, trisomic, triploid, tetrasomic) all refer to various types of chromosomal variations due to nondisjunction or other errors during cell division.