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The reason why you don’t see solid or liquid oxygen is because oxygen is a natural occurring gas. Gas can not be solid or liquid because there is too much energy to have volume/shape. That’s why you see oxygen tanks, as the tank keeps the gas contained and that is why you can’t see it in the air outside or in something like H20 (water).
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Just don’t open the link in the other answer. It’s a scam...
The material that has been widely used in casting has been copper. Thus, option C is correct.
Casting has been the process of molding the liquid into a specific shape with the mold. The casting involves the heating of elements and converting them into liquid. The liquid has been poured into the mold and cooling results in the casted material.
The casted material has been selected based on the boiling temperature, cooling temperature, resistivity, cost-effectiveness, and damping ability.
The material that has been consisted of these characteristics has been copper. Thus, copper has been commonly used for casting. Thus, option C is correct.
For more information about casting, refer to the link:
brainly.com/question/1253405
It is not directly over a flame because it depends on the substance you might not want to heat it too much.you never know what could happen
It is a.combination that is the correct answer i think