Viscosity refers to the resistance to movement. This could be due to various factors: the structure of the molecules, intermolecular forces, and the surface on which the fluid is traveling. I'm not sure if you're referring to the atmospheric pressure or the vapor pressure, but the vapor pressure a fluid exerts mainly depends on the strength of the intermolecular forces. So you could say that viscosity and pressure could technically be related in terms of intermolecular forces but you would need more information and this probably goes beyond the scope of the mcat. On a side note, the questions stem stated that the fluid is of the same mass density. If you were to replace it with a higher density such as replacing water with mercury then you'd have a lower fluid level since mercury is more compact.