Step 1: Understanding the Concept
Clove oil contains eugenol, a phenolic compound (4-allyl-2-methoxyphenol).
Step 2: Action of eugenol
Eugenol acts as a local analgesic that reduces pain and also kills microbes, so it relieves toothache and prevents infection.
Step 3: Compare
Curcumin is found in turmeric, methyl salicylate in wintergreen oil, and gallic acid in tea and gall nuts.
So the reason is eugenol.
Final Answer:
Clove helps toothache because eugenol has analgesic and antimicrobial properties.
\[ \boxed{\text{(B) }\text{Eugenol, present in it, exhibits analgesic and antimicrobial properties.}} \]