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1 mark question

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Explanation:

Helium belongs to group VIII of the periodic table "Noble gases". It has only 1 electronic shell and that too contains 2 electrons according to the accommodation of the shell. Hence, it's electronic shell is complete. This is the reason, Helium is chemically unreactive.

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in cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. a contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes.

explanation: