What is a harmful effect of electrical resistance?

Resistance resist the flow of current. This means that if 5V go through a resistance, it'll be reduce down to something below or equal to 5V.

If it gets reduce below 5V, lets say it goes down to 3V, the extra 2V must go somewhere. That 2V energy is converted to heat and dissipated through the resistor.

If there's a big current then the energy dissipated will be huge. And more negery = more heat which can cause fire and burn you.

1.solid

2.carbon dioxide

3.helium