Why are the elements fluorine (f), chlorine (cl), and bromine (br) all found in the same group within the periodic table? they all exist as gases at room temperature. they all react with the noble gases. they have similar chemical properties. they are all non-metals that form 1+ ions.

indicate valleys, hills, steepness and gentleness of slopes.

explanation:

contour lines on a map indicate elevation, or depth. numeric notations on contour lines refer to the level of elevation, or height about sea level.

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).