Activation energy is what kind of chemical reaction that absorbs energy

Activation energy is the energy required by reactants to undergo chemical reaction and given products

Every reactant has some internal energy (sum of all kind of energy like kinetic energy, potential energy, mechanical energy, chemical energy etc). It needs some extra energy to undergo chemical reaction which is activation energy

All kinds of reaction whether exothermic or endothermic needs activation energy

Threshold energy = internal energy + activation energy

the answer for sodium is 0.186

the answer for rubidium is 0.251

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.