Final answer:
The plural form of 'una cena popular' is 'unas cenas populares'.
Step-by-step explanation:
The plural form of 'una cena popular' is 'unas cenas populares'.
In Spanish, when the noun is feminine singular, like 'cena' (meaning dinner), the plural form is formed by changing the 'a' to 'as' at the end of the noun, and adding the article 'unas' (meaning some) before the noun.
For example, 'una escuela' (meaning a school) becomes 'unas escuelas' (meaning some schools).
Learn more about Plural form in Spanish