Complex sentence: The condition is hyperkalemic because a high extracellular potassium ion concentration will make it even more unfavourable for potassium to leave the cell in order to repolarise it to the resting potential, and this further prolongs the sodium conductance and keeps the muscle contracted.
Split into simpler sentences: The condition is hyperkalemic because a high extracellular potassium ion concentration will make it even more unfavourable for potassium to leave the cell to repolarise it to the resting potential. This further prolongs the sodium conductance and keeps the muscle contracted.