There are three main types of energy transfer:
Conduction is used to describe energy transfer (thermal energy), in solids, so heat is transferred from the hotter side of a solid to the colder part, and this is done by vibrating the molecules in this solid object
Convection is like conduction but in liquids and gases, exactly like in our question, when we have water being heated, the particles in the bottom will be heated, and then will become less dense and go to the top, making the cold particles go to the bottom and be heated, and this process will occur many times in liquids and gases
Radiation does not involve particles, but instead will be about electromagnetic radiation, therefore it will be transferred by waves and not particles
In our question we have:
X = Convection
Y = Conduction
Z = Radiation