Elements that have similar properties are typically found in the same group or column of the periodic table.
- F (Fluorine) and Ne (Neon) are both in Group 17 and Group 18, respectively, and have different properties (F is a halogen, Ne is a noble gas).
- Ca (Calcium) and Sc (Scandium) are in different groups (Group 2 and Group 3, respectively).
- Li (Lithium) and Fr (Francium) are both alkali metals in Group 1.
- Cs (Cesium) and Rn (Radon) are also in different groups (Group 1 and Group 18).
The pair that has the most similar properties is Li (Lithium) and Fr (Francium) because they are both alkali metals in Group 1 of the periodic table.
So, the correct answer is Li and Fr.