An orange powder coating the bottom of rivers from water runoff through old coal mines is called acid mine drainage.

False.

Explanation:

Acid mine drainage is a phenomenon that begins when rocks containing sulfide minerals are removed from the interior of the earth by mining activities and, when disposed on the earth's surface, oxidize by reaction with atmospheric water and oxygen. The acidic (and not powder) solutions generated by the acidic drainage of the mines, as they penetrate rocks and soils, can solubilize some chemical elements present, and can contaminate surface waters such as rivers, streams and / or groundwater.

Although acid drainage can be accompanied by erosive processes, these are quite different phenomena. While erosion refers to the removal and transport of solid sediments, usually in suspension by rainwater runoff, acid drainage is the movement of solutes in acidic waters, not necessarily by runoff.

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.  

read more on -

request for reexamination