The right answer is d).The cell is eukaryotic because it has chloroplasts.
Chloroplasts (or plastids) are present in all eukaryotic plant cells (with the exception of some unicellular species that lack them). These are membrane-bound elements, located in the cytoplasm of the cell, containing chlorophyll and providing photosynthesis.
Since diatoms are unicellular organisms of a plant nature, they possess chloroplasts, the number of which varies according to the species from one to several tens, and which may have the form of grains, plates, bands or even stars.