In angiosperms, various processes are involved in the reproduction and fertilization stages. One such process is the fusion of the male gamete with the egg cell, which is crucial for the formation of a zygote. This process is known as syngamy.

Explanation of Options:

1. Double Fertilization: Double fertilization is a hallmark of angiosperms and involves two distinct fertilization events. One male gamete fuses with the egg cell forming the zygote (syngamy), while the other fuses with two polar nuclei to form the triploid primary endosperm nucleus. Thus, syngamy is part of double fertilization but not equivalent to it.
2. Syngamy: Specifically refers to the fusion of the male gamete (sperm cell) with the egg cell, resulting in the formation of a diploid zygote. This is the direct answer to the question.
3. Fragmentation: Fragmentation is a form of asexual reproduction where a new organism grows from a fragment of the parent. It does not involve gametes or fertilization processes.
4. Pollination: Pollination is the transfer of pollen from the male anther to the female stigma. It leads to fertilization but is not the fusion process itself.

From the explanation above, it's clear that the correct answer is Syngamy.

Conclusion: Syngamy plays a pivotal role in sexual reproduction in angiosperms by ensuring that genetic material from the male and female gametes merge, initiating the development of a new plant.