Plzz me asap is it possible for a reaction to be exothermic but not spontaneous? yes, the reaction may require an activation energy. no, all spontaneous reactions are exothermic. y es, all spontaneous reactions are endothermic. no, exothermic reactions never use activation energy.

the ozone layer acts as a filter for the shorter wavelength and highly hazardous ultraviolet radiation (uvr) from the sun, protecting life on earth from its potentially harmful effects. when the sky is clear, there is an inverse relationship between stratospheric ozone and solar uvr measured at the earth's surface.