Restriction endonucleases, also known as restriction enzymes, are enzymes that recognize specific DNA sequences and cleave the DNA at or near these recognition sites. These enzymes are commonly found in bacteria and are part of their defense mechanisms against foreign DNA, such as viral DNA. They play a crucial role in molecular biology and genetic engineering, as they can be used to cut DNA at specific locations and generate DNA fragments with defined ends.

Among the options provided, the restriction endonuclease is Hind II. Here's a detailed explanation:

Hind II:
- Hind II is a type II restriction endonuclease derived from the bacterium Haemophilus influenzae.
- It recognizes and cleaves DNA at a specific palindromic sequence: 5'-AAGCTT-3'.
- The cleavage occurs between the A and the G residues within this sequence, resulting in fragments with sticky ends.
- The recognition site of Hind II is a 6-base pair sequence, which means that it occurs frequently in DNA.
- Hind II is widely used in molecular biology and genetic engineering techniques, such as DNA cloning and recombinant DNA technology.
- It is commercially available and has been extensively studied, making it a popular choice for DNA manipulation.

Other options and their explanations:

(a) DNase I:
- DNase I is an endonuclease that specifically cleaves phosphodiester bonds within DNA molecules.
- However, it is not a restriction endonuclease as it does not recognize specific DNA sequences.
- It cleaves DNA randomly, resulting in a mixture of fragments with various sizes and ends.
- DNase I is commonly used to degrade DNA in experiments where the removal of DNA is desired, such as RNA extraction or chromatin digestion.

(b) RNase:
- RNase refers to a group of enzymes that specifically degrade RNA molecules by cleaving phosphodiester bonds.
- Like DNase I, RNase is not a restriction endonuclease as it does not recognize specific DNA sequences.
- It targets RNA rather than DNA and is used to remove RNA from DNA samples or in RNA-related experiments.

(d) Protease:
- Protease refers to a group of enzymes that catalyze the hydrolysis of peptide bonds in proteins.
- Proteases have no role in DNA cleavage or recognition of specific DNA sequences.
- They are used in various applications, such as protein purification and digestion for protein characterization.

In summary, Hind II is the restriction endonuclease among the options provided. It recognizes a specific DNA sequence and cleaves the DNA at or near these recognition sites, generating DNA fragments with defined ends. DNase I, RNase, and protease are enzymes that target different molecules (DNA, RNA, and proteins, respectively) and do not possess the specific recognition properties of restriction endonucleases.