Sodium Efflux and Osmotic Effects Steps:

• Batrachotoxin increases cell membrane permeability to Na⁺, allowing Na⁺ to exit cells as stated.
• Na⁺ efflux reduces intracellular solute concentration, making the intracellular fluid hypotonic.
• Osmosis then draws water out of the cell to the hypertonic extracellular space, shrinking the cell (statement 1 correct).
• Extracellular space gains Na⁺, increasing its solute concentration (statement 3 correct; statements 2 and 4 likely claim opposite concentration changes, which are incorrect).

Why A is correct:

• Na⁺ efflux lowers intracellular osmolarity (causing water loss and shrinkage, per statement 1) and raises extracellular osmolarity (per statement 3), following osmotic principles where water moves toward higher solute concentration.

Why the others are wrong:

• B: Statement 4 wrongly implies extracellular fluid becomes less concentrated; Na⁺ influx there increases concentration.
• C: Statement 2 wrongly suggests intracellular fluid becomes more concentrated; it becomes less concentrated.
• D: Statements 2 and 4 both misstate concentration changes from Na⁺ efflux.

Final answer: A