If convection in the mantle slowed, which of the following would also slow?

Mantle convection is only a theory, but probably the answer you're looking for is earthquakes/volcanoes.

The correct answer to this open question is the following.

If convection in the mantle slowed, what would also slow is the magma.

When we talk about the geological term "convention in the mantle" we are referring to a method used by the earth to move heat. Indeed, the convection is the way plate tectonics move. Let's remember that this is a natural process on planet earth, and the reason volcanos, mountain ranges, and earthquakes exit. Scientists affirm that convection in the mantle also exists in planets such as Mars.