Final answer:
A polyploid organism has a chromosome number that is an exact multiple of a chromosome set and is usually found in plants, leading to larger and more robust individuals compared to their normal counterparts.
Step-by-step explanation:
The correct answer to the question is b) Polyploid.
An organism is considered polyploid when it has a chromosome number that is an exact multiple of the chromosome set. This condition is different from a euploid organism, which has the chromosomal number specific to its species. Polyploidy often occurs in the plant kingdom and can lead to larger and more robust plants. In contrast, polyploidy in animals is rare and can lead to sterility since an odd number of chromosome sets complicates the meiotic process. For instance, if a diploid egg (which is abnormal because eggs should be haploid) is fertilized by a normal haploid sperm, this yields a triploid zygote which would be sterile due to complications during meiosis. However, when polyploidy results in even chromosome numbers, it can lead to viable and sometimes advantageous conditions in plants.