Which type of material becomes molten rock at subduction zones? light plates, heavy plates, continental crust, or new oceanic crust

The answer is heavy plates.

Let's look into the options one by one

Light plates- this is incorrect.

Light plates will stay above the denser plate when subduction occurs. Although the rock of crust mightbe bended, it will not be subducted under and reach magma and is therefore false.

Heavy plates- this is correct.

Heavy plate is the plate that will be pulled under the less dense plate due to gravity. When the plate reach the magma and can no longer maintain it's solid structure under the heat, the melts and becomes molten rock.

Continential plates- this is incorrect.

Continential plates is a place with less density and is lighter comparing to denser oceanic plate,thus it would not be the plate that subducts under another but the one to stay above, therefore it would not become molten rock.

New oceanic crust- this is incorrect.

The crust that are near subduction zones are usually the oldest crust that gets pushed aside to the zone,while new plate are usually the furthest away from the zone and is therefore not correct.

Hope it helps!