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, 
Answer:
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From mole ratios, the mass ratio of different elements can be predicted. Also the volume can be predicted based on density for liquids and ideal gas law equation for gases. From the mole ratios, the empirical formula can be predicted, as well as the molecular formula given another data which is mass of the sample.
ANSWER IS (A)
EXPLANATION:
Bronsted-Lowry concept states that a substance is an acid if it can act as a H+ donor.
HCl in aqueous solution means that HCl is present in water, HCl + H2O --> H3O+ + Cl-. This reaction will take place, the H+ from HCl will be donated to H2O. So, HCl is a bronsted-lowry acid by definition.
However, Methanol (CH3OH) its written that it is liquid, i.e. pure methanol, CH3OH(l). It is both acidic as well as basic. when it is mixed with water then it behaves as an acid.
The last one ammonia in gas phase is also neutral because its not in water. if mixed in water it behaves as a base.