Answer:
HCN
Explanation:
There are several factors that can tell us when an acid is stronger than another, which are the following:
1. The Polarity of the X - H Bond
2. Size of the X atom.
3. Charge on the acid.
4. Oxidation state of the central atom
5. Values of Ka and pKa.
From all of this factors, we can see that the exercise is already giving us values of Ka, and also we have different types of acid, not only with the form H - X
So, we will base the force of an acid by it's pKa value.
The pKa value which is calculated with the expression:
pKa = -logKa
pKa is a value that indicates how strong is the acid you are working with. This value can vary depending on factors such the charge of the acid. I f this charge can be easily distributed in resonance structures, the compound is more acidic, and therefore the pKa value is lower.
The lower the pKa, the more acidic the compound is.
So calculating the pKa on every structure we have:
HF: pKa = -log(3.5x10^-4) = 3.46
HNO2: pKa = -log(4.6x10^-4) = 3.34
HCN: pKa = -log(4.9x10^-10) = 9.31
HCOOH: pKa = -log(1.8x10^-4) = 3.74
HClO2: -log(1.1x10^-2) = 1.96
So according to all this values, we can conclude that the weakest acid is the HCN
