Are the following compounds or mixtures? Please help to check the answers.

1) starch - compound
2) chalk - compound
3) coal - mixture
4) drain water -compound

I agree with starch, chalk, and coal but I disagree with drain water (although drain water may have compounds in it).

To determine if a substance is a compound or a mixture, we need to understand the definitions of these terms:

- Compound: A compound is a substance made up of two or more different elements chemically combined in a fixed ratio.
- Mixture: A mixture is a combination of two or more substances that are physically mixed but not chemically combined.

Now, let's analyze each substance:

1) Starch: Starch is a complex carbohydrate that is commonly found in plants. It is made up of repeating units of glucose molecules. Since it consists of only one type of molecule (glucose), it is a compound.

2) Chalk: Chalk is a soft, porous sedimentary rock composed mainly of calcium carbonate, which is a compound made of carbon, oxygen, and calcium atoms. Like starch, it is also a compound.

3) Coal: Coal is a fossil fuel formed from the remains of ancient plants. It consists of various organic compounds, such as carbon, hydrogen, and sulfur. Additionally, it may contain impurities like rock fragments and minerals. Hence, coal is considered a mixture.

4) Drain water: Drain water usually refers to the water that has been used to flush or drain through pipes. It contains various dissolved substances like minerals, salts, and sometimes even small amounts of chemicals. Since it is a combination of different substances that are physically mixed together, drain water is a mixture.

So, the correct answers are:
1) Starch - compound
2) Chalk - compound
3) Coal - mixture
4) Drain water - mixture