1.9 understand that atoms consist of a central nucleus, composed of protons and neutrons, surrounded by electrons, orbiting in shells

The answer to this one is kind of in the question, you just need to understand that...

- atoms consist of a central nucleus (there is a nucleus that is in the centre of the atom)
- the nucleus is made up of protons and neutrons (the nucleus has a positive charge due to the positive protons and neutral neutrons)
- electrons orbit the nucleus in shells - the first shell contains two electrons when full, all the others contain 8 when full.