While showing some common compounds used in our daily life in the laboratory, the teacher showed sodium chloride compound and told that it is also called common salt. Next day, one of the students brought common salt from home to the laboratory and requested the teacher to show sodium chloride as well. He kept both common salt and sodium chloride in two different watch glasses and left. Next day, during lunch break the student went to the laboratory and saw that the common salt brought from home became sticky whereas the compound sodium chloride remained as it is. What would be the justification given by the teacher for the above observation?

Explanation

### Step-by-Step Solution:

1. **Understanding Common Salt and Sodium Chloride**:
- Common salt, which is often used in cooking, is chemically known as sodium chloride (NaCl). However, the common salt available in the market may contain other minerals and impurities.

2. **Composition of Common Salt**:
- The common salt brought from home may contain additional compounds such as magnesium chloride (MgCl2) and calcium chloride (CaCl2). These compounds are hygroscopic, meaning they can absorb moisture from the air.

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