Answer
Option C.
Step-by-step explanation
The given dissociation of HF is shown below:
HF(aq) + H₂O(l) ⇌ H₃O⁺(aq) + F⁻(aq)
Hence, the equation for the acid dissociation constant Kₐ, of HF will be:
![K_a=([H_3O^+][F^-])/([HF])](https://img.qammunity.org/2023/formulas/chemistry/college/hsv1a8zys7mxqcsaaooj6peowzkgsys9ym.png)
The reason that water (H₂O) does not appear in Ka is that the activity of water is assumed to be very nearly equal to 1.
Hence, the correct answer is option C.