One of the hazards facing humans in space is space radiation: high energy charged particles emitted by the sun. During a solar flare the intensity of this radiation can reach lethal levels. One proposed method of protection for astronauts on the surface of the moon or Mars is an array of large electrically charged spheres placed high above areas where people live and work. The spheres would produce a strong electric field E to deflect the charge particles that make up space radiation. The spheres would be similar in construction to a Mylar balloon, with a thin electrically conducting layer on the outside surface on which a net + or-charge would be placed. A typical sphere might be 5m in diameter. Required:
To repel electrons in the radiation from a solar flare each sphere must produce an Electric field 1 x 10^6 N/C at 25 m from the center of the sphere. What net charge on sphere is needed?

answer: the correct answer is 1.

explanation: there are various process in which a radioactive nuclei decays:

1) alpha decay: in this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle. the mass number is reduced by 4 units.

2) electron capture: in this decay process, a parent nuclei absorbs an electron and gets converted into a neutron. simply, a proton and an electron combines together to form a neutron. mass number does not change in this process.

3) gamma ray emission: it is a decay process in which an unstable nuclei gives excess energy by a spontaneous electromagnetic process. this decay releases . this process does not change the mass number.

4) positron emission: it is a type of decay process, in which a proton gets converted to neutron and an electron neutrino. this is also known as -decay. in this the mass number remains same.

from the above information, we see that only alpha-decay is producing a change in the mass number of the nucleus.

the answer for apex is the lowest