Question

Good students are respectful ____all

Answer 1

Explanation:

good students are respectful to all

Answer 2

Good students are respectful to all.

Here the blank should be filled with an adjective. as an adjective is a word that describes the noun. "all" here is a noun. We need a word to describe the noun. "to" is acting as an adjective here.

Therefore, to is the correct word suitable for the given blank.