Which one of the following accurately describes the force of gravity?

a. the force of gravity is slightly lower at the bottom of a mountain than it is at the top.
b. the gravity acceleration has no effect on a body moving in directly the opposite direction of the force of gravity.
c. the gravity acceleration is in the same direction as the force of gravity, and thus toward the center of the earth.
d. the gravity acceleration is in the same direction as the force of gravity, and thus away from the center of the earth.

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.