Answer to Question 1
ANS: D
Because water follows the osmotic gradients established by changes in salt concentration, water balance is tied to sodium balance, not that of potassium, chloride, or bicarbonate.
Answer to Question 2
ANS: A
Osmotic forces determine water movement between the ECF and ICF compartments.
Oncotic pressure pulls water at the end of the capillary, which makes it move between intra and extra as interstitial is considered extra. The antidiuretic hormone regulates water balance, which would make water move between the intra- and extracellular spaces. Buffer systems help regulate acid balance.