The correct answers are: Magnesium and Iron.
The mantle layer is the layer that is located just bellow the crust. This is a layer that has much higher temperatures and pressure than the ones on the surface, as well as the rock being all heated and in big portion being in magma form. This is also the layer that produces the convection currents that in turn create all the geologic activity on the surface.
The dominant two components of the mantle layer are the magnesium and the iron which are found in big amounts in the silicate rocks. These are also the main ingredients in the magma that manages to penetrate to the surface.