Atoms and Nuclei — Radioactivity, Half-Life, and Why Fission and Fusion Both Release Energy

Rutherford's gold-foil experiment ended with one strange sentence: almost everything went straight through, but a few alpha particles bounced back. That bounce proved the atom is mostly empty space with a tiny, dense, positively charged centre. The nucleus is about one hundred-thousandth the size of the atom, yet it carries more than 99.9% of its mass.

That is not trivia — it is why this chapter is worth marks. Nuclear questions sit in the general-science block of almost every competitive paper, and they repeat in a narrow band: which radiation penetrates most, what happens to the atomic number after a decay, a one-line half-life calculation, and what makes a reactor different from the Sun.

None of it needs advanced physics. It needs about fifteen facts held firmly enough that you do not hesitate between two options that look alike. The next three cards are those fifteen facts, and the two after that show exactly how papers disguise them.

1. Arrange alpha, beta and gamma radiation in decreasing order of penetrating power.

2. A radioactive sample of 160 g has a half-life of 3 hours. How much of it remains undecayed after 12 hours?

3. When a nucleus emits a beta particle, what happens to its atomic number and mass number?

4. The energy radiated by the Sun is produced mainly by:

5. In a nuclear reactor, control rods are usually made of cadmium or boron because these materials:

6. Carbon dating using carbon-14 is suitable for determining the age of:

7. Two atoms are isotopes of each other. This means they have:

8. Binding energy per nucleon is highest for nuclei in the region of: