The periodic table houses noble gas elements in group 18. these elements are highly stable and rarely react with any other elements. what is one possible reason for the stability of the noble gas elements?

a.

they easily form covalent bonds.

b.

the compounds that they form with other elements are very unstable.

c.

their outermost shell has the maximum number of electrons that it can hold.

d.

they require less activation energy

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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only about ten percent of the energy at one trophic level is passed on to organisms at the next trophic level. the remainder of the energy is used in life processes or lost as heat.

the nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and dna, the building blocks of all life. plants absorb nitrogen in the form of ammonium, nitrate ion and, on rare occasions, as amino acids. animals receive nitrogen necessary for biological processes from feeding on living or dead organic matter.