Which of the following is not a pure substance?
1. milk
2. oxygen
3. water
4. carbon dioxide
1. milk
To determine which of the options is not a pure substance, we need to understand what a pure substance is. A pure substance is a type of matter that has a fixed or definite composition and distinct properties. It consists of only one type of atom or molecule.
Now, let's analyze each option:
1. Milk: Milk is not a pure substance because it is a mixture of various components such as water, proteins, fats, lactose, vitamins, and minerals. It contains different types of molecules and is not made up of a single type of substance.
2. Oxygen: Oxygen is a pure substance because it consists only of oxygen molecules (O2). It is an element and does not contain any other type of molecule.
3. Water: Water is another pure substance. It is made up of water molecules (H2O) and does not contain any other types of molecules.
4. Carbon dioxide: Carbon dioxide is also a pure substance. It consists of carbon dioxide molecules (CO2) and does not contain any other types of molecules.
Therefore, the answer to the question is that all of the options (1. milk, 2. oxygen, 3. water, and 4. carbon dioxide) are pure substances.