Here is the image and read the q from description.

Saurabh 1 Best Answer

Yes A, B and D would be correct option here .As island arc is related to subduction settings and the convex side of the respective island arc is towards ocean (best example is your Aleutian chain of islands). While when it comes to gravity anomalies this is something that is very vast and related to geophysics especially. Gravity anomalies arises due to density contrast Or density difference between the subsurface body and their parent lithology. If the density of subsurface body is greater than the parent lithology, then it's negative gravity while if it is less than parent, then a positive gravity anomaly. Gravity anomalies in turn depends on the mass excess and mass deficit. So mass excess leads to positive gravity anomaly and mass deficit leads to negative gravity anomaly(this gravity anomaly was reason that scientist used to claim the large crater of an asteroid that killed dinosaurs, chicxulub crater under the marine body). In case of subduction (as in mountain chains and island arcs) , the gravity anomaly is low (negative gravity anomaly) due to mass deficit at the depth or in subduction zones(note that subduction zone is a destructive plate boundary so if one considers a isostasy case then mass excess at the surface must be balanced by the mass deficit in the subsurface or at depth, cuz that's how your gravitational equilibrium establish). from the figure attached below you can clearly observe that island arc is convex downward or convex towards ocean).