To determine which two elements most likely have similar properties, we can look at their positions in the periodic table.
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F (Fluorine) and Ne (Neon): These elements are in different groups; Fluorine is a halogen (Group 17) and Neon is a noble gas (Group 18).
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Cs (Cesium) and Rn (Radon): Cesium is an alkali metal (Group 1) and Radon is a noble gas (Group 18).
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Ca (Calcium) and Sc (Scandium): Calcium is an alkaline earth metal (Group 2), while Scandium is a transition metal (Group 3).
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Li (Lithium) and Fr (Francium): Both are alkali metals and belong to Group 1 of the periodic table.
Given this analysis, the best answer is:
Li and Fr, as both belong to the same group (alkali metals) and are likely to have similar properties.