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.

the atomic mass is the bottom number on the element.

-steel jelly

the awnser is group 12