All the examples you've provided illustrate effects related to the movement of Earth's tectonic plates, but they showcase different processes. If you're looking specifically for an example that best shows the effects of tension (which relates to stretching of the Earth's crust), the most appropriate choice would be:
4. the mid-Atlantic Ridge splitting Iceland.
This is because the mid-Atlantic Ridge is a divergent boundary where the Eurasian and North American plates are moving apart, creating tension and resulting in volcanic activity and the formation of new crust. The other examples illustrate different interactions like compression (Himalayas and Andes Mountains) or lateral movement (San Andreas Fault).