Why pH 6.8 is used in stacking gel?

pH 6.8 is used in stacking gel in electrophoresis because it helps the proteins remain negatively charged. pH 6.8 is more acidic than the pH 8.8 of the separating gel. This acidic pH implies a lower ionic strength and consequently highly electrical resistance. This enables the proteins to move through the gel matrix more efficiently without being overly affected by their charge.