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choose the correct statement with respect to a fuel cell:
a. it produces higher emissions than biodiesel - powered vehicles.
b. it combines hydrogen and oxygen to produce water, and in the process produces electricity and heat.
c. a fuel cell produces a voltage of about 1,000 volts.
d. fuel cells are heavy and increase vehicle load.

Explanation:

• Option a: Fuel cells are known for their relatively low emissions compared to many traditional power sources like some diesel - based systems. Biodiesel - powered vehicles may have higher emissions in some aspects (e.g., particulate matter in some cases), so this option is incorrect.
• Option b: In a fuel cell, hydrogen reacts with oxygen. The overall reaction is \(2H_2+O_2 = 2H_2O\). During this electrochemical reaction, electrical energy and heat are also produced. This is a correct description of the basic operation of a fuel cell.
• Option c: A single fuel cell typically produces a voltage in the range of 0.6 - 1.2 volts. To get higher voltages, fuel cells are stacked. So, a single fuel cell does not produce 1000 volts. This option is incorrect.
• Option d: Fuel cells are designed to be relatively lightweight compared to some traditional power storage or generation systems (e.g., large internal combustion engines with their associated cooling, fuel storage, etc.). So, this option is incorrect.

Answer:

B. It combines hydrogen and oxygen to produce water, and in the process produces electricity and heat.