1. 3 protons, 4 neutrons, 3 electrons. Lithium
2.
| Radiation | What it is | Range | Stopped by |
| Alpha (a) | Helium nucleus (NOT atom) | 1 cm in air | Skin, sheet of paper |
| Beta (b) | High speed electron | 50 cm in air | 3 mm aluminium sheet |
| Gamma (g) | Electromagnetic radiation | Infinite | Several cm lead |
3.
The atomic number is the number of protons
The mass number is the number of protons and neutrons.
4.
| Element | Mass Number | Atomic Number | Neutrons |
| Uranium 238 | 238 | 92 | 146 |
| Uranium 235 | 235 | 92 | 143 |
| Plutonium | 233 | 94 | 139 |
5. Alpha is positive (+2); beta is negative (-1); gamma has no charge.