Which statement is true about the law of conservation of energy for an object released from a certain height above the ground? a. in the absence of any external forces and at any point, the kinetic energy and the potential energy are always equal. b. in the absence of any external forces and at any point, the kinetic energy is always greater than the potential energy. c. in the absence of external forces and at any point, the potential energy is always greater than the kinetic energy. d. in the absence of external forces and at any point, the sum of the kinetic energy and the potential energy is always constant.

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.