The average thickness of the ozone layer in the stratosphere is approximately 300 Dobson Units (DU).

Introduction / Context:
The ozone layer in the stratosphere absorbs harmful ultraviolet radiation and is commonly quantified using Dobson Units (DU). A global, long-term climatological average is often cited near 300 DU, though it varies with latitude and season.

Given Data / Assumptions:

• We are asked for the typical average stratospheric ozone column.
• Units are in Dobson Units (DU).
• Accept reasonable global mean around 300 DU.

Concept / Approach:
1 DU corresponds to a 0.01 mm thick layer of pure ozone at standard temperature and pressure. Climatological studies place the global mean near 300 DU, higher at mid to high latitudes and lower near the tropics.

Step-by-Step Solution:

Verification / Alternative check:
Satellite and ground-based data (e.g., Dobson spectrophotometers) routinely report climatological means near 300 DU, with normal variability ±50–100 DU by region/season.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing local episodic values with global means; misinterpreting DU as a height or pressure level rather than a column amount.

Final Answer:
300 DU