Which one of the following hydrolyses internal phosphodiester bonds in a polynucleotide chain ?

The enzyme that hydrolyzes internal phosphodiester bonds in a polynucleotide chain is an endonuclease. Endonucleases are a class of enzymes that cut the phosphodiester bond within a polynucleotide chain, as opposed to exonucleases, which remove nucleotides from the ends of a DNA or RNA molecule. Lipase is an enzyme that hydrolyzes lipids, and protease is an enzyme that hydrolyzes proteins. Therefore, the correct answer is option (C) Endonuclease. Think of it this way: endonucleases are responsible for cutting within a DNA or RNA molecule, which is essential for various molecular biology applications, including DNA cloning and sequencing.