Because flame provides a source of heat so that the magnesium metal atoms can overcome their activation energy. Activation energy is the minimum energy required in order for a chemical reaction to proceed. When the magnesium metal burns it reacts with oxygen found in the air to form Magnesium Oxide.
Answer:
Mescarinic and Nicotinic
Explanation:
Postganglionic fibers can be present in both sympathetic and parasympathetic divisions, their main difference resides in how in the sympathetic division the postganglionic fibers are adrenergic and use norepinephrine (noradrenalin) as a neurotransmitter, in the parasympathetic division, on the other hand, fibers are cholinergic and use acetylcholine as a neurotransmitter, the<em> postganglionic neurons of sweat glands release acetylcholine for the activation of muscarinic receptors, another kind of receptor for acetylcholine are nicotinic receptors </em>that act as transmembrane sodium/potassium channels, while muscarinic receptors need to act through intracellular proteins.
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The incoming and outgoing energy at the Earth’s surface must balance. Or in other words, the flow of energy into the atmosphere must be balanced by an equal flow of energy out of the atmosphere and back to space.<span>
Earth's Energy balance describes how the incoming energy from the sun is used and returned to space. All </span>of the energy entering earth’s atmosphere comes from the sun. Half of it is absorbed by the earth’s surface i.e. the land and oceans, 30% is directly reflected back to space by clouds and 20% is absorbed by the atmosphere and clouds.<span>Earth's </span>actual<span> average global temperature is around 14° C (57 F).</span>
Radioactivity in our world <span>b. is as old as the universe.
</span><span>Radioactive atom spontaneously emits energetic particles or waves, while decays on lighter nuclei (atoms with smaller atomic mass). Radioactivity is used to calculate how old is Earth and living things, for that purpose isotope of carbon is used.</span>
