Answer:
9000 BC
Explanation:
Although various copper tools and decorative items dating back as early as 9000 BCE have been discovered, archaeological evidence suggests that it was the early Mesopotamians who, around 5000 to 6000 years ago, were the first to fully harness the ability to extract and work with copper.
Answer:
c. contraction
Explanation:
Heating will cause substances to expand, or change their state (like solid to liquid) or it may be a chemical reaction.
It is called a polyatomic ion.
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Answer:
Atomic emission spectrum came out by a series of colored lines
Explanation:
When electricity is passing through an element or when it is viewing through a prism, a unique spectra of light emitted by an element is called atomic emission spectra. They are acting as an element of finger print because they are unique. When we are seeing a set of colored lines or a black background , it is an emission spectrum. If we are watching black lines on a colored background it is absorption spectrum. In electromagnetic spectrum the visible portion are the colors.
In nucleus electrons can exist in some areas are known as shells. Shell corresponds an energy level that is designed by a quantum number n. The lowest energy level electrons are close to the nucleus.
An atom is shone by light, its electrons absorbs photons and it gain energy, and jump to higher level.
