Grinding of wheat grain changes its size . It is a ________ change.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Change**: The question asks about the grinding of wheat grain and how it affects the substance. When we grind wheat grains, we are altering their size.

2. **Identifying the Type of Change**: Changes in substances can be classified into two categories: physical changes and chemical changes.

3. **Defining Physical Change**: A physical change is one where the form or appearance of a substance changes, but its chemical composition remains the same. For example, when ice melts into water, it changes form but is still H2O.

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