Imagine that in another universe, atoms and elements are identical to ours, except that atoms with six valence electrons have particular stability (in contrast to our universe where atoms with eight valence electrons have particular stability). Give an example of an element in the alternative universe that corresponds to each of the following.
a. a reactive mental
b. a reactive non-mental
c. a noble gas

NB: This answer is based on the assumption that, just like our universe, in this alternate universe, the innermost shell of elements is filled first, and is stable with just two electrons.

A reactive metal will be a metal element that has one electron less than that needed to achieve valency. The metal will tend to want to gain electron from a non-metal to achieve a stable outer shell. For aluminium, a metal, with an atomic number of 13; in this alternate universe, the electronic configuration will be 2, 6, 5. The outermost shell will need an additional electron from a non-metal to achieve valency, making it very reactive with a non metal.

A reactive non-metal will have its outermost shell having just one electron, the non-metal will tend to want to lose this electron to a metal to achieve valency with the already filled inner shell. For Florine, a non-metal, with an atomic number of 9; in this alternate universe, the electronic configuration will be 2, 6, 1. Losing the outermost electron, to a metal, frees up the inner complete stable shell, making it very reactive with a metal.

A noble gas is an element, usually in gaseous form, that has a complete outer shell, and hence has no need for gaining or losing extra electron(s). In an alternate universe, Oxygen, will have an electronic configuration of 2, 6. This is stable and hence it does not react with other elements.