Avery famous scientist explains a recently observed natural phenomenon with a new theory. should the new theory be considered valid?

No

Explanation:

A theory is an adequately research explanation of observation that is in accordance with modern scientific methods. The theory should have undisputable empirical supports in form of scientific experiment which has rigorously and comprehensively proven the theory using scientific method and other scientists should also have similar observations when the theory is tested. As such the famous scientists phenomenon needs to be subjected to serious scientific testing before it can be established as theory.

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.