The smallest organelle you would have problems viewing would be the ribosome. Ribosomes are the sites of protein production, and are the most abundant organelle within cells. They are tiny, however, when compared with larger organelles, such as the nucleus. Another organelle that is usually too small to be seen with a light microscope is the mitochondrion. The mitochondrion is the "power plant" in animal cells, the site where cellular respiration takes place. Depending on the type of cell and its energy requirements, there can be lots of mitochondria or few mitochondria. Lastly, the lysosome can be rather difficult to see within the confines of a light microscope. Lysosomes are the "sanitation department" of the cell, taking care of disposing everything from foreign invaders to waste products produced by the cell during its life processes.
Golgi bodies,mitochondria,lysosomes, endoplasmic reticulum.hope it helps