How did elements with more than 2 protons, such as the carbon in our cells, form? a. they formed 400 million years after the universe formed in giant fusion reactors known as stars.
b. they formed from hydrogen and helium slamming into each other in the first few minutes after the big bang.
c. they are formed when lighter elements are pulled together by gravity to form a planet.
d. they were formed at the same time as hydrogen and helium right after the big bang.

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.