Final answer:
The correct process for a radioactive isotope that decomposes by K-electron capture is the combination of one of its electrons with a proton to form an additional neutron.
Step-by-step explanation:
A radioactive isotope that decomposes by K-electron capture emission combines one of its electrons with one of its protons, creating an additional neutron. This process occurs because the neutron-to-proton ratio within the nucleus is too low for stability. Essentially, the electron capture converts a proton into a neutron, which adjusts the balance between the neutrons and protons and hence the stability of the nucleus.
Other forms of decay, such as beta decay, involve the transformation of a neutron into a proton and the emission of an electron, while positron emission is the conversion of a proton into a neutron along with the emission of a positron, a positively charged electron. Alpha decay involves the release of a helium nucleus, but that is not the process described in the question. Therefore, the most accurate answer to the questionnaire description is: (a) combines one of its electrons with one of its protons creating an additional neutron.