Question 3
volcanic islands and island chains, like the hawaiian islands, were created by
(need an answer here) spots, which may or may not occur on
a plate's boundary.
question 4
a crack in the crust near iceland is what is thought to have started the breakup of
pangaea. this crack created the (need answer here)
ocean. as that ocean expanded, the (need answer here)
ocean shrank in size.

3. Hot spots , 4. S shaped mid oceanic ridge,  pacific ocean.

Explanation:

The Hawaiian islands are located on the hotspots that are formed by the collision of two strong plates and the presence of volcanoes and high magnitude earthquakes as the pacific plate is continuously moving on the western side as its subducting under the North American plate and hence shrinking in size. The s-shaped Atlantic ocean has mid atlantic ridge and as this ocean spreads the lava is up welding across the ocean floor and hence the opening of the atlantic plate is seen.