No, the word "open" does not have a long vowel. It is pronounced with a short /o/ sound.

I think yes because the -y- is acting like a vowel and an open syllable is when nothing comes after the vowel.

Fro exmaple the word he. We say that the vowel is open.

The enunciated vowel is "O", OH-PEN. The other vowel in the spelling is the "E".

The word "hello" has an open syllable. An open syllable ends in a vowel sound and usually has a long vowel sound. In "hello," the first syllable "hel" ends in a long vowel sound.

No

he

she

me

sky

hi

...any word that does not have a consonant after the vowel leaving the vowel to make its long sound.