**Core Concept**
The question requires identification of a specific species of Plasmodium based on the characteristics of the schizonts and pigment present in the blood smear. This involves understanding the morphological features of different Plasmodium species and their corresponding clinical manifestations.

**Why the Correct Answer is Right**
The presence of all stages of schizonts with 14-20 merozoites and yellowish-brown pigment is characteristic of Plasmodium vivax. This is because P. vivax schizonts are known to have a large number of merozoites (typically 14-24) and contain a yellowish-brown pigment called hemozoin, which is a byproduct of hemoglobin digestion. The presence of all stages of schizonts indicates that the parasite is actively reproducing, which is consistent with the biology of P. vivax.

**Why Each Wrong Option is Incorrect**
**Option A:** Plasmodium falciparum typically has a small number of merozoites (usually 8-24) and contains a dark brown pigment called hemozoin. Additionally, P. falciparum schizonts are usually not seen in peripheral blood smears due to sequestration in capillaries.
**Option B:** Plasmodium malariae has a smaller number of merozoites (typically 6-12) and does not contain a yellowish-brown pigment. The schizonts of P. malariae are also larger and more elongated than those of P. vivax.
**Option D:** Plasmodium ovale has a similar number of merozoites to P. vivax, but the schizonts are smaller and contain a more brownish pigment.

**Clinical Pearl / High-Yield Fact**
It's worth noting that the presence of all stages of schizonts in a blood smear is often referred to as "multiple schizogony" and is a characteristic feature of P. vivax infections. This is because P. vivax has a longer incubation period and a more gradual onset of symptoms, allowing for the development of multiple generations of schizonts.

**✓ Correct Answer: C. Pl. vivax**