5. with the largest atoms and the smallest number of valence electrons and with the smallest atoms and the greatest number of valence electrons are the most reactive.

We have to fill the gap

The correct answer is: Metals with the largest atoms and the smallest number of valence electrons and non-metals with the smallest atoms and the greatest number of valence electrons are the most reactive.

Reactivity of any species depends on ease of release or gain of electron. The species which can release electron easily from valence shell, the species is more reactive whereas the species which can accept electron to its valence shell easily is also more reactive.