How an atom reacts chemically depends on how willing it is to share electrons with others.
It’s electrons
Given is the ratio of conjugate base and conjugate acid of phosphoric acid. pH of a substance is the concentration of the hydrogen ions in its solution and higher this concentration lower is the value of pH.
pKa value is a measure of the strength of acid, it is the negative log of acid dissociation constant Ka.
Just to make sure I’m right, is number 1 miss spelled??
For a reaction to occur, there should be mobility of ions in reactant side.
If the reactant is larger, its mobility will be lesser than that of smaller ones.
So reactants smaller in size have higher mobility which makes reaction faster.
Hence D is the correct option.
Hope this helps, have a great day/night ahead!