Scientists have hypothesized that oxygen began to build up in the earth's atmosphere after the development of living things with the ability to
a. breathe air.
b. form tissues.
c. photosynthesize.
d. reproduce sexually.

c. photosynthesize.

Explanation:

It is believed that it was life itself that originated all this oxygen present on the planet and promoted the change in the composition of the earth's atmosphere. This change would have begun, according to paleontologists, when the ability to perform photosynthesis emerged during the evolution of living beings. Commonly associated with plants, the ability to produce oxygen is also common to bacteria such as blue algae, unicellular beings that live in the oceans and, despite their name, are more similar to bacteria than algae. The great virtue of photosynthesis is to convert sunlight and carbon dioxide into energy for metabolism. As a byproduct, oxygen is released.

the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.