If both the assertion and reason are true but the reason is not a correct explanation of the assertion
The largest cell of the embryo sac is central cell. It consists of highly vacuolate cytoplasm which is rich in reserve food and golgi bodies. In the middle, the cell contains two polar nuclei which have large nucleoli. The polar nuclei fuse to form a single diploid secondary or fusion nucleus.
Hence, the correct option is (B)