How is an electrolytic cell different from a voltaic cell?
electrons are gained at the anode in an electrolytic cell.
oxidation occurs at the cathode in an electrolytic cell.
a power supply is needed in an electrolytic cell.
a salt bridge is needed in an electrolytic cell.

C is the correct answer. A voltaic cell is an electrochemical cell that uses a chemical reaction to produce electrical energy. An electrolytic cell is an electrochemical cell that drives a non-spontaneous redox reaction through the application of electrical energy, but it needs a power source.

the answer is either b or c

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.