All metals are highly reactive because of their properties. As you move left on a period while moving down you move close to Francium (most-metallic).
Since group 1 is the most farthest left group, it is the most metallic, therefore the most reactive.
Francium.
group 1
In terms of reactivity, Potassium(K) is the most reactive element among group 1 elements.
Fr or Francium is the most reactive alkali metal (group 1)
The least reactive metal in Group 1 of the periodic table is francium. Francium is a highly radioactive and rare element that has very little practical use due to its extreme reactivity with other elements.
The most reactive goup in the metals is the Alkali metals (Group I) The most reactive non-metal group is Group 17 or VIIA) the Halogens. It is difficult to say which of the two groups is more reactive. Chemists will say that Flourine is the most reactive element. Note that Group 18 is the least reactive, most stable.
In Group 1, cesium (Cs) is expected to be the most reactive element, as reactivity increases down the group due to the increasing atomic radius and the decreasing ionization energy. In Group 2, barium (Ba) is typically the most reactive, as reactivity also increases down this group for similar reasons—larger atomic size and lower ionization energy. Both cesium and barium readily lose their outermost electrons, making them highly reactive.
The most reactive metals of the periodic table are those that belong to alkali group. Among this group, the more electrons contain each atom of each element, the more reactive it is. This is why Francium is the most reactive of alkali metals.
The most reactive element of part of Group 1 is the one with the highest atomic number. If hydrogen is considered to be in period 1, then the answer to the question is sodium. If instead hydrogen is considered to be in a 0th period, then the answer to the question is potassium.
Alkali metals (group 1) and the Halogens (group 17)
Group 1, the Alkali Metals, which are extremely reactive.
The group containing the most reactive elements is Group 1, also known as the alkali metals. These elements include lithium, sodium, and potassium, which are highly reactive due to their low ionization energies and tendency to lose electrons to form positive ions.