A: Element (single, identical atoms)

Here are the solutions to the remaining questions:

2.2

• A: Element (single, identical atoms)
• B: Mixture (two different types of atoms, not bonded in a fixed ratio)
• C: Compound (identical molecules, each made of two different types of atoms bonded together)
• D: Element (identical molecules, each made of three identical atoms bonded together)
• E: Mixture (two different types of molecules: one element, one compound)
• F: Element (identical molecules, each made of two identical atoms bonded together)
• G: Mixture (two different types of atoms, not bonded in a fixed ratio)
• H: Compound (identical molecules, each made of two different types of atoms bonded together)
• I: Mixture (two different types of molecules: one element, one compound)

2.3

2.3.1

• (a) 1:1: NaCl (Sodium chloride)
• (b) 2:1: H₂O (Water)
• (c) 1:2: CO₂ (Carbon dioxide)
• (d) 2:1:4: H₂SO₄ (Sulphuric acid)

2.3.2
The ratio in CaCO₃ (Calcium Carbonate) is:

• Calcium (Ca): 1
• Carbon (C): 1
• Oxygen (O): 3 The ratio of Ca:C:O is $\boxed{\text{1:1:3}}$.