'Once in a blue moon' means
AEvery day
BVery rarely
COn full moon nights
DEvery blue moon party
Answer & Solution
Correct answer: B. Very rarely
1. A 'blue moon' is a rare lunar event.
2. Idiom denotes extreme rarity.
3. Every day is the opposite.
4. Hence option A.
_Source: jkchrome.com SSC Idioms and Phrases PDF (Mistral OCR), section on common idioms_