How does modern periodic table explain the cause of periodicity.

The cause of periodicity in properties is the repetition of similar outer electronic configuration after certain regular intervals. For example, all the elements of group 1 i.e. alkali metals have a similar outer electronic configuration, ns1.

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:

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