Błędnie: In quantum physics, most of the phenomenons are difficult to describe in intuitive terms. Poprawnie: In quantum physics, most of the phenomena are difficult to describe in intuitive terms.
Słowo ‘phenomenon’ znaczy „fenomen”, „zjawisko”, a liczba mnoga tego słowa to ‘phenomena’, np. ‘Many X-files type phenomena could be scientifically explained’ („Wiele fenomenów w stylu archiwum X można by wyjaśnić naukowo”).