Step 1: Formula for hand positions.
- Minute hand position (in degrees from 12 o’clock) $= 6 \times M$.
- Hour hand position (in degrees from 12 o’clock) $= 30 \times H + 0.5 \times M$.
Here $H$ = hour, $M$ = minutes.
Step 2: Find the positions at 4:20.
Minute hand: $6 \times 20 = 120^\circ$.
Hour hand: $30 \times 4 + 0.5 \times 20 = 120 + 10 = 130^\circ$.
Step 3: Difference between hands.
$|130^\circ - 120^\circ| = 10^\circ$.
\[
\boxed{10^\circ\ \text{(Option (b)}}
\]