What is the cause of voltage drop across a resistor?
The heat dissipation and volt drop are related, but I would not describe the dissipation as the cause of the drop. As electrons pass through a resistance, they lose energy as they interact with electrons in the conducting material. As energy is given up to the material, it gains thermal energy so its temperature rises. The moving electrons lose potential energy and hence there is a drop in voltage. This is similar to a gas passing through a narrow pipe, losing pressure and causing heating by friction.