which of these elements could be described as a monoatomic substance held together by london's forces?

Question

sodium, silicon, tetrachloromethane, argon, potassium bromide

Answer 1

Van der Wall's forces are intermolecular forces that arise from electron clouds acting like dipoles (or multipoles in some molecules).

Noble gases cannot interact in the "classical" chemical reactions. However, atoms of Noble gases (e.g., argon) can "stick" together because of the van der Wall's force.
"The electron cloud at any moment takes the shape of an ellipsoid around the nucleus, leaving a slight negative charge on one side of the major axis and a slight positive charge on the other."

If it were not for that effect, it would be impossible to liquefy noble gases.

Other "chemical" effects are normally stronger than the London Force. However, as the atom's electron clouds gets bigger (atoms with high atomic numbers), the London Force may be less disadvantaged.

My vote goes to argon. Na and Si are probably too small. The other two are not monoatomic.