Why is electron capture accompanied by the emission of an x-ray?

  During electron capture, an inner electron usually from K shell or L shell combines with proton of the nucleus thereby changing proton to neutron. The process of electron capture is also accompanied by the emission of neutrino. It generally occurs in proton rich nucleus. The capture of electron by the proton creates a hole in the electron shell. The hole created is generally filled by the dropping down of a higher level electron with the emission of X -ray.

- both b and d.

-since b and d are the closest coastlines then that makes it the most affected.

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a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.