Fertilizer sacks have a three- number value called the NPK value written on them. What does the NPK stand for (18-24-12 written on the bag)?

it's a label number

Explanation:

Every label carries three conspicuous numbers, usually right above or below the product name. These three numbers form what is called the fertilizer's N-P-K ratio — the proportion of three plant nutrients in order: nitrogen (N), phosphorus (P) and potassium (K).

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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uh two lol