This question is about elements, compounds, and mixtures.
Which type of substance is clean, dry air?
The diagrams in Figure 1 represent different substances using circle models.
◯\bigcirc◯ and ∙\bullet∙ represent atoms of two different elements.

Using Figure 1: Which diagram represents a pure compound?
Using Figure 1: Which diagram represents a mixture of two elements?
Substances can be separated from mixtures using different methods. State the method used to separate a mixture of different coloured pigments in food colouring.
A liquid mixture containing three hydrocarbons with boiling points of 36∘C36^\circ\text{C}36∘C, 69∘C69^\circ\text{C}69∘C, and 98∘C98^\circ\text{C}98∘C is separated by fractional distillation. Which hydrocarbon distils and is collected first?