Compared to the surrounding material, mantle plumes rise toward earth’s surface from the core-mantle
boundary because they are
(1) cooler and less dense (3) hotter and less dense
(2) cooler and more dense (4) hotter and more dense

Compared to the surrounding material, mantle plumes rise towards the Earth's surface from the core-mantle boundary because they are hotter and less dense (3) than the surrounding material.  A mantle plume is a large column of hot rock that rises through the earth's mantle. This plume is hot enough to cause the rocks in the lower lithosphere to melt. When the plume reaches the bottom of the lithosphere, it spreads out forming a mushroom shape cap. The lithosphere is then pushed up and stretched out. This forms magma chambers which feed the surrounding surface volcanos. 

Answer sinking and cooled;