Why Fr is the most reactive metal ?

Francium is hypothesized to be the most reactive metal, but so little of it exists or can be synthesized, and the longest half-life of its most abundant isotope is  

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minutes, so that its reactivity cannot be determined experimentally.

Explanation:

Francium is an alkali metal in group 1/IA. All alkali metals have one valence electron. As you go down the group, the number of electron energy levels increases – lithium has two, sodium has three, etc..., as indicated by the period number. The result is that the outermost electron gets further from the nucleus. The attraction from the positive nucleus to the negative electron is less. This makes it easier to remove the electron and makes the atom more reactive.

Experimentally speaking, cesium (caesium) is the most reactive metal.

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explanation:

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