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