In the Layers panel, turn on Borders and Labels and also Gallery > Volcanoes, then double-click on the Problem 7 placemark. Divergent boundaries often begin as triple junctions composed of three rift "arms" at ~120° apart (which may or may not evolve into divergent boundaries). Knowing that rifts (red lines) generally open perpendicular to the rift (or sub-parallel to the light blue transform faults), which of the statements below about this area is incorrect? a. the NW-trending Red Sea is a linear sea that is opening in a NE-SW direction
b. the ENE-trending Gulf of Aden is a linear sea that is opening in a NNE-SSW direction
c. the volcanoes in Africa define a narrow linear rift that is opening in a NW-SE direction
d. the volcanoes in Africa define a volcanic arc related to subduction off Africa's east coast

d. the volcanoes in Africa define a volcanic arc related to subduction off Africa's east coast

Explanation:

Many crust plates move over the mantle. These plates are limited by three types of ridges or borders that differ in the movement they produce.

Boundaries types: Divergent, Convergent, and Transforming.

Divergent boundary: Occurs along with an underwater mountain range, known as the mid-oceanic ridge or divergent ridge. New crust is created by the molten materials rising from the mantle. The two plates at each side of the rift separate, and the stream of hot material creates a new seabed between them. It occurs an expansion of the sea bottom, which separates the plates. The divergence direction is transversal to the rift orientation.  Old plates get separated, and the new crust instantaneously gets formed. The emerging mantle occupies the space left by the separation of the two plates.

a. the NW-trending Red Sea is a linear sea that is opening in a NE-SW direction.  CORRECT →  The diverging direction is perpendicular to the rift orientation.

b. the ENE-trending Gulf of Aden is a linear sea that is opening in a NNE-SSW direction. CORRECT

c. the volcanoes in Africa define a narrow linear rift that is opening in a NW-SE direction. CORRECT.  

d. the volcanoes in Africa define a volcanic arc related to subduction off Africa's east coast ⇒ INCORRECT. The collision between plates creates volcanic arches and continental arches. This process belongs to the convergent boundaries, in which two oceanic plates collide, or one oceanic plate crushes with a continental one.