To determine which two elements are most likely to have similar properties, we can look at their positions in the periodic table.
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Ca (Calcium) and Sc (Scandium): They are in different groups (Calcium is in Group 2 and Scandium is in Group 3), so they don't have similar properties.
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Li (Lithium) and Fr (Francium): Both are in Group 1 (alkali metals). They have similar chemical properties because they are in the same group.
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F (Fluorine) and Ne (Neon): Fluorine is a halogen (Group 17) and Neon is a noble gas (Group 18), so they do not have similar properties.
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Cs (Cesium) and Rn (Radon): Cesium is an alkali metal (Group 1) and Radon is a noble gas (Group 18), so they do not have similar properties.
Based on this analysis, the two elements that most likely have similar properties are Li and Fr (Lithium and Francium).