Step 1: Recall the relationship between HCF and LCM.
For any two positive integers $a$ and $b$, the product of the two numbers is equal to the product of their HCF (Highest Common Factor) and LCM (Least Common Multiple).
\[
a \times b = \text{HCF}(a, b) \times \text{LCM}(a, b)
\]
Step 2: Verification with example.
Let $a = 12$ and $b = 18$.
Then, $\text{HCF}(12, 18) = 6$ and $\text{LCM}(12, 18) = 36$.
Now, check:
\[
\text{HCF}(a, b) \times \text{LCM}(a, b) = 6 \times 36 = 216
\]
and
\[
a \times b = 12 \times 18 = 216
\]
Both sides are equal, hence the relation holds true.
Step 3: Conclusion.
Therefore, the correct relation between $a$, $b$, $\text{HCF}$, and $\text{LCM}$ is:
\[
a \times b = \text{HCF}(a, b) \times \text{LCM}(a, b)
\]