What is hail stones?why is oxygen ​

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Explanation:

hailstones --> Hail is a type of precipitation, or water in the atmosphere. Hail is formed when drops of water freeze together in the cold upper regions of thunderstorm clouds. These chunks of ice are called hailstones. Most hailstones measure between 5 millimeters and 15 centimeters in diameter, and can be round or jagged.

i am sorry i can not answer the oxygen question because it is not all there.

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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1.the evidene of the reaction

2.yes

3.yes