Two planes orthogonal to a third plane are parallel F 2. Two lines parallel to a plane are parallel T 3. A plane and a line either intersect or are parallel T 4. Two lines parallel to a third line are parallel T 5. Two planes either intersect or are parallel F 6. Two planes parallel to a line are parallel F 7. Two lines either intersect or are parallel F 8. Two planes orthogonal to a line are parallel F 9. Two lines orthogonal to a plane are parallel T 10. Two planes parallel to a third plane are parallel F 11. Two lines orthogonal to a third line are parallel.

an obstruction

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.