B

According to Faraday's laws of electrolysis, the amount of substance decomposed during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte. This relationship can be expressed mathematically as:
$$ m = k imes Q $$
where:
- $m$ is the mass of the substance decomposed,
- $Q$ is the total electric charge passed,
- $k$ is a proportionality constant known as the electrochemical equivalent.
Thus, the amount of decomposition is proportional to the electrochemical equivalent of the substance, making Option B the correct answer.