Explanation:

Malaria is a mosquito-borne infectious disease caused by parasites of the genus Plasmodium. There are four main species of Plasmodium that cause malaria in humans: P. vivax, P. ovale, P. malariae, and P. falciparum. Each species has its own unique characteristics and life cycle.

The arrangement of merozoites, which are the reproductive forms of the parasite, can be used to differentiate between the different species of Plasmodium.

P. vivax:
In the case of P. vivax, the merozoites are arranged in a circular or rosette-like pattern within the infected red blood cells. This arrangement is known as Schüffner's dots or Schüffner's stippling. The merozoites form clusters or aggregates, giving the appearance of a target or bull's eye within the infected red blood cells. This characteristic arrangement of merozoites is specific to P. vivax.

P. ovale, P. malariae, and P. falciparum:
On the other hand, P. ovale, P. malariae, and P. falciparum do not exhibit the circular arrangement of merozoites seen in P. vivax. Instead, the merozoites in these species are arranged in a more irregular or scattered manner within the infected red blood cells.

P. falciparum:
In the case of P. falciparum, the merozoites are often seen as a cluster or "banana-shaped" arrangement called Maurer's clefts. This is a key characteristic of P. falciparum and helps differentiate it from other species.

In summary, the circular arrangement of merozoites is specific to P. vivax, while the other species (P. ovale, P. malariae, and P. falciparum) do not exhibit this characteristic arrangement. Therefore, the correct answer to the given question is option 'A' - P. vivax.