The correct answer is (D) Mysteries; secrets; information known only to those involved, particularly involving alchemical research. Also, a secret and powerful remedy, or a great secret of nature, which alchemists attempted to discover.

Arcana, the plural form of Arcanum, comes from Latin arcere (to shut in).

Examples of use:

• Arcana that captivated alchemists included the change of metal to gold.
• Finding an elixir of life was among the arcana that preoccupied alchemists.