Learn Italian: Questi ristoranti sono molto buoni. - These restaurants are very good.

Ristoranti is the plural of ristorante. Nouns that end in -e in the singular change to -i in the plural, no matter their gender! Ristorante is masculine, but because the -e ending doesn't give away the gender like -o or -a usually does, you just have to memorize the gender when you learn the word.

Why do we use questi instead of queste here?

Questi is the masculine plural word for "these". Even though ristorante belongs to the -e group of nouns, it is still a masculine noun. Therefore, the word for "these" must take the masculine plural form questi to match it.

Why does the adjective buoni end in -i instead of -e if the singular noun is ristorante?

Adjectives follow their own normal rules, even if the noun belongs to the -e group. The word for "good" is buono, which is a standard adjective that ends in -o in the singular. To match a masculine plural noun like ristoranti, it takes the standard masculine plural ending -i, making it buoni.

Why doesn't molto change to molti to match the plural noun ?