What is the minimum maintenance requirement for a long margin account containing only common stock?

The correct answer is B, 25%. The minimum maintenance requirement for a long margin account holding common stock is established by FINRA Rule 4210, which requires that investors maintain at least 25% equity in the account relative to the current market value of the securities.

This requirement is different from the initial margin requirement, which is set by Regulation T of the Federal Reserve and is typically 50% for purchasing securities. Once the position is established, the maintenance requirement ensures that the investor continues to have sufficient equity in the account to support the borrowed funds.

If the equity in the account falls below 25% due to a decline in the value of the securities, the investor will receive a maintenance (margin) call, requiring them to deposit additional funds or securities to bring the account back into compliance.

Choice A (5%) is far too low and not a regulatory standard. Choice C (50%) refers to initial margin, not maintenance. Choice D (75%) is not a recognized requirement.

Thus, the correct minimum maintenance requirement for long margin accounts with common stock is 25%, making choice B correct.