Step 1: Understanding Font Weights.
In typography, "weight" refers to the thickness of the characters. The most common font weights are:
- Hairline: A very thin weight, usually the thinnest in a font family.
- Bold: A thicker, heavier weight, commonly used for emphasis.
Step 2: Conclusion.
Thus, the weights in a font family are Hairline and Bold.
\[
\boxed{\text{The correct answer is (a) Hairline, (b) Bold.}}
\]