Adjectives vary in Italian depending on the gender of the noun they refer to and whether it’s singular or plural.
We can divide them into two main groups depending on their ending.
il libro costoso – i libri costosi (the expensive book/s)
la penna rossa – le penne rosse (the red pen/s)
The adjectives of this group are the most common:
il ragazzo intelligente – i ragazzi intelligenti (the intelligent boy/s)
la storia interessante – le storie interessanti (the interesting story/ies)
There are fewer adjectives in this group but some of them are still very common: