What common characteristic is generally shared by the elements at the center of a period?

The common characteristic that is shareed by the elements found at the center of a period would be that they are the least reactive species. Having lower value of electronegativity, there is less ionization of the atoms which would also contribute to less reactivity.

Least reactive.

Explanation:

The elements in the center of periodic table are least reactive, generally.

They are less electronegative and electropositive as well.

They do not lose electrons easily as they have high ionization energy to act as metals. Also they have low electron affinity as compared to non metals.

Thus they are very less reactive.

it's filtration, but this is an assumption so my apologies if i got this

1. they vary with a higher number because boiling is way hotter than melting