Complex sentence: The pK a of a compound is determined by many things, but the most significant is the stability of the conjugate base, which is determined mainly by the ability (or inability) of the conjugated base to stabilize the negative charge.
Split into simpler sentences: The pK a of a compound is determined by many things, but the most significant is the stability of the conjugate base. This is primarily determine by the ability (or inability) of the conjugated base to stabilize negative charge.