How do we come to know that a chemical reaction has taken place?

Explanation

To determine if a chemical reaction has taken place, we can look for several key indicators. Here’s a step-by-step explanation of how we can identify a chemical reaction:

### Step 1: Formation of New Products
When two or more substances react, they often form new substances. The formation of a new product is one of the most straightforward indicators of a chemical reaction. For example, when sodium (Na) reacts with oxygen (O2), it forms sodium oxide (Na2O).

**Hint:** Look for changes in the composition of substances involved in the reaction.

### Step 2: Change in State
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