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The problem is asking which of the following mathematical expressions is *not* true. Let's analyze each option one by one:

**Option (A):**  
\[
(7 + 8) + 9 = 7 + (8 + 9)
\]
Both sides of the equation use the associative property of addition, which states that the way in which numbers are grouped in addition does not affect the sum. Therefore:
\[
(7 + 8) + 9 = 15 + 9 = 24
\]
\[
7 + (8 + 9) = 7 + 17 = 24
\]
So, this statement is true.

**Option (B):**  
\[
(7 \times 8) \times 9 = 7 \times (8 \times 9)
\]
This equation uses the associative property of multiplication, which means the grouping of factors does not affect the product. Therefore:
\[
(7 \times 8) \times 9 = 56 \times 9 = 504
\]
\[
7 \times (8 \times 9) = 7 \times 72 = 504
\]
This statement is also true.

**Option (C):**  
\[
7 + 8 \times 9 = (7 + 8) \times (7 + 9)
\]
First, evaluate the left-hand side (LHS) and the right-hand side (RHS):
- On the LHS:
\[
7 + 8 \times 9
\]
Following the order of operations (PEMDAS/BODMAS), multiplication is done before addition:
\[
8 \times 9 = 72, \quad \text{then} \quad 7 + 72 = 79
\]

- On the RHS:
\[
(7 + 8) \times (7 + 9) = 15 \times 16 = 240
\]
Since \(79 \neq 240\), this statement is false.

**Option (D):**  
\[
7 \times (8 + 9) = (7 \times 8) + (7 \times 9)
\]
This equation uses the distributive property of multiplication over addition:
\[
7 \times (8 + 9) = 7 \times 17 = 119
\]
\[
(7 \times 8) + (7 \times 9) = 56 + 63 = 119
\]
This statement is true.

### Conclusion:
The incorrect statement is **Option (C)**.

Would you like more details on any of the concepts, or do you have any other questions?

Here are 5 related questions:
1. How does the associative property work in different operations?
2. What is the distributive property of multiplication over addition?
3. How do order of operations affect calculations in complex expressions?
4. Can you explain how to apply the associative property to algebraic expressions?
5. Why is the order of operations important in mathematical expressions?

**Tip:** Remember, when evaluating expressions, always follow the order of operations: Parentheses, Exponents, Multiplication and Division (from left to right), and Addition and Subtraction (from left to right).

Explore the associative and distributive properties in mathematics with detailed examples. Learn how these properties affect calculations and solve problems using real-world scenarios. Suitable for students in Grades 6-8.

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