Answer : The acid dissociation constant Ka of the acid is, 
Explanation :
First we have to calculate the concentration of hydrogen ion.
![pH=-\log [H^+]](https://tex.z-dn.net/?f=pH%3D-%5Clog%20%5BH%5E%2B%5D)
Given: pH = 4.06
![4.06=-\log [H^+]](https://tex.z-dn.net/?f=4.06%3D-%5Clog%20%5BH%5E%2B%5D)
![[H^+]=8.71\times 10^{-5}M](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D8.71%5Ctimes%2010%5E%7B-5%7DM)
The dissociation of acid reaction is:

Initial conc. c 0 0
At eqm. c-cα cα cα
Given:
Degree of dissociation = α = 0.10 % = 0.001
![[H^+]=c\alpha](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3Dc%5Calpha)


The expression of dissociation constant of acid is:
![K_a=\frac{[H^+][A^-]}{[HA]}](https://tex.z-dn.net/?f=K_a%3D%5Cfrac%7B%5BH%5E%2B%5D%5BA%5E-%5D%7D%7B%5BHA%5D%7D)

Now put all the given values in this expression, we get:


Thus, the acid dissociation constant Ka of the acid is, 
Explanation:
Given the amount of fluorine is ---- 1.25 mol.
What is the mass of given fluorine in grams?
Since

To get the mass of the substance in grams, multiply the given number of moles with the molecular mass of the substance.
Hence, among the given options, the correct answer is the last option that is
Multiply the atomic mass of fluorine by 1.25.
Hydrogen bonding occurs between a hydrogen atom and an electronegative atom (e.g., oxygen, fluorine, chlorine). The bond is weaker than an ionic bond or a covalent bond, but stronger than van der Waals forces (5 to 30 kJ/mol). A hydrogen bond is classified as a type of weak chemical bond.