**Core Concept**
The lifecycle of Plasmodium species involves a complex interplay between the human host and the mosquito vector. In the case of Plasmodium vivax, the parasite undergoes a process of gametogenesis within the mosquito, resulting in the formation of infective stages that can be transmitted to humans through mosquito bites.

**Why the Correct Answer is Right**
The infective stage for mosquito in Plasmodium vivax is the gametocyte, specifically the male and female gametocytes. The male gametocytes, also known as microgametocytes, undergo a process called exflagellation, where they release a flagellated spermatozoid that fertilizes the female gametocyte, resulting in the formation of a zygote. The zygote then undergoes a series of transformations, ultimately resulting in the formation of sporozoites, which are the infective stage for mosquito. The female gametocytes, also known as macrogametocytes, provide the necessary nutrients for fertilization and subsequent development of the zygote.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the sporozoite is the infective stage for humans, not the mosquito.
* **Option B:** This option is incorrect because the schizont is a stage of the parasite's lifecycle within the human host, not the mosquito.
* **Option C:** This option is incorrect because the trophozoite is a stage of the parasite's lifecycle within the human host, not the mosquito.

**Clinical Pearl / High-Yield Fact**
It's essential to note that Plasmodium vivax has a dormant liver stage, known as hypnozoites, which can cause relapses of the disease. This is a key difference between P. vivax and other Plasmodium species.

**Correct Answer:** C.