A teacher takes the top and a side off a box. She cuts a hole in another side and puts a candle outside the box, as shown below 25 am 25 cm When the teacher lights the candle in a dark room, some of the candlelight shines through the hole. Which diagram best shows how the light appears on the opposite wall of the box? 25 cm 25 cm 25 cm 25 cm B 25 cm 25 cm 25 cm 25 cm A B C D​

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.