An isotonic solution contains equal solute concentration on both sides.

Choice A reason: The client with an ileostomy is at risk for fluid volume deficit because an ileostomy is a surgical opening in the ileum, the last part of the small intestine, that allows the drainage of intestinal contents. This can result in a loss of fluids and electrolytes, especially sodium and potassium, which can lead to dehydration and hypovolemia.

Choice B reason: The client with cirrhosis is not at risk for fluid volume deficit, but rather fluid volume excess. Cirrhosis is a chronic liver disease that causes scarring and impaired liver function. This can lead to portal hypertension, which is an increase in the pressure in the portal vein that carries blood from the digestive organs to the liver. Portal hypertension can cause ascites, which is the accumulation of fluid in the abdominal cavity, and edema, which is the swelling of the tissues due to fluid retention.

Choice C reason: The client with heart failure is not at risk for fluid volume deficit, but rather fluid volume excess. Heart failure is a condition where the heart is unable to pump enough blood to meet the body's needs. This can lead to congestion of the blood vessels, which can cause pulmonary edema, which is the accumulation of fluid in the lungs, and peripheral edema, which is the swelling of the extremities due to fluid retention.

Choice D reason: The client with decreased renal function is not at risk for fluid volume deficit, but rather fluid volume excess. Decreased renal function is a condition where the kidneys are unable to filter the blood and remove excess fluids and wastes. This can lead to oliguria, which is a decrease in urine output, and anuria, which is the absence of urine output. This can cause fluid overload, which can affect the heart and the lungs.

Choice A reason: This is incorrect because diffusion is the movement of solutes (dissolved substances) from an area of higher concentration to an area of lower concentration, until equilibrium is reached.

Choice B reason: This is incorrect because hydrostatic pressure is the force exerted by a fluid against a wall or a membrane. Hydrostatic pressure can drive the movement of fluid and solutes across a membrane, but it is not the movement itself.

Choice C reason: This is correct because osmosis is the movement of a pure solvent (liquid) across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration, until equilibrium is reached.

Choice D reason: This is incorrect because ATP is not a movement, but a molecule. ATP stands for adenosine triphosphate, which is the main source of energy for cellular processes. ATP can provide energy for some types of transport across membranes, such as active transport.