To determine which layer has the least amount of density, we need to consider the general densities of the items listed.
- Bolt - Metals like bolts generally have high density.
- Vegetable oil - This has a moderate density, less than metals.
- Ping pong ball - Made of plastic, it typically has a low density and is lighter than both a bolt and vegetable oil.
- Popcorn kernel - While it can be light, when popped, it becomes very light and fluffy, having a very low density compared to its unpopped state, but as a whole, the unpopped version still has a moderate density.
Considering this information, the "ping pong ball" typically will have the least density compared to the other items listed. However, if we consider popped popcorn as a separate state, it would have an even lower density.
If the question refers to the standard state of the items, the most appropriate answer would be ping pong ball. But if popped popcorn is considered, then that would be the correct choice for the least density.
Without the context of whether popcorn is popped or unpopped, based on typical densities:
- Ping pong ball is the best answer if not accounting for kernels being popped.