Step 1: The prokaryotic 70S ribosome is made of a 30S small subunit and a 50S large subunit.
Step 2: The 30S subunit carries the 16S rRNA, while the 50S subunit carries two rRNA molecules, the 23S and the 5S rRNA, along with about 34 proteins.
Step 3: Since the question asks about the 50S subunit, the second rRNA alongside 5S is 23S, so option (C) is correct.