¿prefieres esta flauta o en la mesa?

a.
ése
b.
éste
c.
ésa
d.
éstos

The answer is: C. ¿Prefieres esta flauta o ésa en la mesa.?

Since the noun is a feminine singular object and it's far, the proper option is ésa/that.

- Do you prefer this flute or that flute on the table?

- ¿Pefieres esta flauta o ésa flauta en la mesa?

The other given options don't fit since:

A. ése/that: Even it's a singular and far demonstrative pronoun, it's referring to a masculine noun.

B. éste/this: It's a singular demonstrative pronoun too, but it's referring to a near masculine noun.

D. éstos/these: It's a plural demonstrative too, but it's referring to plural and near masculine noun.

Have a nice day!