Explanation:

Clathrates are compounds in which guest molecules are trapped in a lattice-like structure formed by host molecules. These compounds are commonly formed between water and various gases, including noble gases. However, not all noble gases have the ability to form clathrates.

Helium (He) is the noble gas among the options provided that does not form clathrates. Here's why:

1. Size and shape:
Clathrate formation depends on the size and shape of the guest molecule. Helium is the smallest noble gas and has a very low molecular weight, making it difficult for it to form stable clathrate structures. Its small size allows helium atoms to easily escape from the lattice, resulting in unstable clathrate structures.

2. Intermolecular forces:
Clathrate formation also depends on intermolecular forces between the host and guest molecules. Noble gases have weak intermolecular forces due to their full outer electron shells, making it difficult for them to form strong interactions with water molecules. Helium, in particular, has extremely weak intermolecular forces and does not readily interact with water molecules, further hindering clathrate formation.

3. Experimental evidence:
Experimental studies have shown that helium does not form stable clathrate structures under normal conditions. Unlike other noble gases such as argon, xenon, and krypton, helium does not exhibit the ability to form clathrates with water or other host molecules.

Overall, the small size, weak intermolecular forces, and lack of experimental evidence all indicate that helium does not form clathrates.