In vanilla Minecraft, which of the following cannot be made into a block?

The answer is Charcoal because it is not naturally found as a solid block in Vanilla Minecraft. Charcoal is a fuel source that is obtained by smelting wood logs in a furnace. While it can be used for various purposes in the game, such as fuel for smelting or crafting torches, it cannot be directly transformed into a block like other materials such as stone, wood, or even coal.