A combination of common salt and iron filings is a mixture.

Explanation:
Definition of a Mixture:
A mixture is a combination of two or more substances that are physically combined and can be separated by physical means. The substances in a mixture retain their individual properties and do not undergo any chemical reaction.

Components of the Mixture:
In the given combination of common salt and iron filings, we have two substances present:
1. Common salt (Sodium Chloride): It is a compound composed of sodium and chlorine atoms. It is commonly used as a seasoning agent in cooking.
2. Iron filings: These are small pieces of iron that have been finely divided. Iron is a chemical element with the symbol Fe and is known for its magnetic properties.

Physical Properties:
Both common salt and iron filings have different physical properties:
1. Common salt: It is a white crystalline solid, soluble in water, and has a salty taste.
2. Iron filings: They are dark gray in color, have a metallic luster, and are attracted to magnets.

Separation of Components:
Since common salt and iron filings are physically combined in the mixture, they can be separated by physical means. Here are two methods that can be used to separate the components:
1. Magnetic separation: Iron filings can be separated from the mixture using a magnet. The magnet attracts the iron filings, leaving behind the common salt.
2. Dissolution and filtration: The mixture can be dissolved in water to dissolve the common salt. The resulting solution can then be filtered to separate the insoluble iron filings.

Conclusion:
Based on the above explanation, it can be concluded that a combination of common salt and iron filings is a mixture because the substances are physically combined and can be separated by physical means without undergoing any chemical reaction.