Gastric acid
The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
Alkaline mucus
Mucus that serves a protective function against acidic environments generally has a high viscosity, though the thickness and viscosity of the mucus layer can vary due to several factors. For example, alkaline mucus in the stomach increases in thickness when the stomach is distended. The pH level of the mucus also plays a role in its viscosity, as higher pH levels tend to alter the thickness of the mucus, making it less viscous. Because of this, invading agents such as "Helicobacter pylori", a bacterium that causes stomach ulcers, can alter the pH of the mucus to make the mucus pliable enough to move through. Exposure to atmospheric air also tends to increase the pH level of alkaline mucus.