(a) Stars are formed inside a cloud of gas and dust in space. When a star forms, the cloud first becomes smaller as it collapses.

1. (a)(i)State what causes the gas cloud to collapse.[1]
2. (a)(ii)Eventually nuclear fusion occurs in the star. State two conditions required for nuclear fusion to occur in the star. 1. 2.[2]
3. (b)(i)When a large star explodes, nuclei of heavy elements are formed. One such nucleus is uranium-235 (²³⁵₉₂U). State the name and the number of each type of particle found in one nucleus of ²³⁵₉₂U.[2]
4. (b)(ii)State one feature that is the same for the nuclei of all isotopes of uranium.[1]
5. (b)(iii)A nucleus of ²³⁵₉₂U in a nuclear reactor can undergo nuclear fission. Describe the process of nuclear fission in a nuclear reactor.[2]
6. (b)(iv)State one difference between nuclear fusion and nuclear fission.[1]
7. (b)(v)The nucleus of ²³⁵₉₂U is not stable. It decays by the emission of an alpha-particle (α) into a nucleus of thorium (Th). Complete the nuclear equation that represents this decay. ²³⁵₉₂U → ____Th + ____₂α[2]
8. (c)(i)Geiger and Marsden carried out an experiment to investigate the scattering of alpha-particles. Fig. 11.1 shows a diagram of the apparatus that they used. When an alpha-particle strikes the fluorescent screen a flash of light is emitted. On Fig. 11.1, mark with a letter P where most flashes occur on the screen.[1]
9. (c)(ii)Describe what is seen on the other parts of the screen.[1]
10. (c)(iii)State two conclusions about atoms of gold that resulted from this experiment.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.