Hello!
To determine the Kb of gallic acid is actually very simple.
The
dissociation reaction of Gallic Acid (HGal) is the following:
HGal+H₂O ⇄ H₃O⁺ + Gal⁻The equation for converting from Ka to Kb is the following:
So, the Kb is
2,19*10⁻¹²Have a nice day!
Significant figures are the digits that come after the first non-zero digit. The second value has 11 significant figures and is therefore the correct answer. However, the fourth answer has 4 significant figures and would also be a correct answer. So I don’t know if perhaps there has been a typo or a mistake in the question but with what you have provided here, both these answer have more than 2 significant figures.