Questions & Answers about Gli zaini neri sono pesanti.
Why do we use gli instead of i for "the"?
How do I pronounce the article gli?
Why is it neri and not nero?
Adjectives in Italian must match the noun they describe in both gender and number. Since zaini is a masculine plural noun, the singular adjective nero (black) changes its ending to match, becoming neri.
The dictionary says "heavy" is pesante. Why does it change to pesanti here?
Adjectives that end in -e in the singular change their ending to -i in the plural. This rule applies whether the noun is masculine or feminine! Since there are multiple backpacks, pesante becomes pesanti.