What is the voltage across a 2-ohm resistor if a current of 0.5 amperes flows through it?
Why Ohm's Law in the form E = I x R gives voltage when you know current and resistance. Here 0.5 amperes times 2 ohms equals 1 volt. Whenever the question gives you current and resistance and asks for voltage, you multiply.
Watch out The 0.25 volt choice comes from dividing the current by the resistance instead of multiplying, which is what you would do if you were solving for something else entirely.
Voltage question = multiply: E = I x R. Current and ohms go together as a product, never a quotient.