Which of the following is not property of a parallelogram ?

Options

A. Opposite sides are congruent.
B. Consecutive angles are supplementary.
C. Diagonals are congruent.
D. Opposite sides are parallel.

Answer

To determine which of the following is not a property of a parallelogram, we will analyze each option systematically.

### Step-by-Step Solution:

1. **Understanding the Properties of a Parallelogram**:
A parallelogram is a quadrilateral with specific properties. The main properties include:
- Opposite sides are equal in length.
- Opposite angles are equal.
- Consecutive angles are supplementary (sum to 180 degrees).
- The diagonals bisect each other.
- Opposite sides are parallel.

2. **Analyzing Each Option**:
We will check each option provided in the question to see if it aligns with the properties of a parallelogram.

- **Option A: Opposite sides are congruent**.
- In a parallelogram, opposite sides are indeed equal in length. Therefore, this option is a property of a parallelogram.

- **Option B: Consecutive angles are supplementary**.
- In a parallelogram, the sum of the measures of consecutive angles is 180 degrees. Thus, this option is also a property of a parallelogram.

- **Option C: Diagonals are congruent**.
- In a parallelogram, the diagonals are not necessarily equal. They can be of different lengths. Therefore, this option does not represent a property of a parallelogram.

- **Option D: Opposite sides are parallel**.
- By definition, in a parallelogram, opposite sides are parallel. Hence, this option is a property of a parallelogram.

3. **Conclusion**:
After analyzing all the options, we conclude that **Option C: Diagonals are congruent** is not a property of a parallelogram.

### Final Answer:
**Option C is the correct answer as it is not a property of a parallelogram.**

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