Ribosomes that occur exclusively in mitochondria is
a)	70 S	b)	55 S	c)	30 S	d)	50 S

(b)

Besides DNA, a mitochondrion has RNA and its ribosomes also. Thus, a complete protein synthesising machinery is present in mitochondria. The ribosomes of mitochondria are small,  55-60 S type, with a large subunit of 40 S and a small subunit of 30 S. The large subunit contain 16-17 S and 5S RNA and the small subunit 12-13 S RNA.