A friend tells you that she has invented a motor that you just add a tiny bit of gasoline to once and then the motor works forever as the kinetic energy and potential energy just keep transforming back and forth indefinitely. Why might you be skeptical

Entropy increases over time

Explanation:

Whereas energy is conserved, applying the principle of conservation of energy, it is true that the kinetic energy will be transformed into potential energy and vice versa. This is ignoring minor losses. However, over time, entropy increases so addition of gasoline just once may not work over a long time.

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.