One atp molecule's hydrolysis releases 7.3 kcal/mol of energy (∆g = −7.3 kcal/mol of energy). if it takes 2.1 kcal/mol of energy to move one na+ across the membrane (∆g = +2.1 kcal/mol of energy), how many sodium ions could one atp molecule's hydrolysis move?

One ATP molecule's hydrolysis can move 3 ions of Sodium (Na+) across the menbrane.

Explanation:

As you can see, the energy provided by ATP is enough for moving 3 ions of Na+. Each ion needs +2.1 kcal/mol of energy.

If we multiply by 3 the energy for moving across the membrane= +6.3 kcal/mol

By adding the energy from ATP:

ΔGTotal=6.3-7.3= -1 kcal/mol