The sole of a gecko's foot is covered with millions and millions of small, dry "hairs" that make direct contact with surfaces, and allow geckos to walk up walls and dangle from the ceiling. Experiments showed that the "hairs" stick well to strongly hydrophobic, strongly hydrophilic, and electrically neutral surfaces and that covalent bonds were not involved. What noncovalent bond is probably involved in the foot adhering to a surface?

Answer: Van der Waals forces

Explanation:

Van der Waals forces are weak intermolecular forces that depend on the distance between two particles. They are caused by correlations in the change in polarization between two nearby particles. To put it in other words, when a particle changes its polarization (becomes more positive on one end and more negative on the other), so does the adjacent particle, and the next one, and so on. This causes these particles to stick together weakly.

The tiny "hairs" increase the surface area of the gecko's feet in contact with the wall, which makes the bond stronger and allows it to support all of its weight.

Because experiments have shown that geckos stick well to both hydrophobic and hydrophilic surfaces, we can assume there aren't any hydrogen bonds present.

Ionic bonds can't be present either because geckos wouldn't stick to electrically neutral surfaces, as these bonds require charged molecules.