Bank Q is most vulnerable to a liquidity crisis due to its significant dependence on short-term repurchase agreements (repos). The proportion of assets pledged as collateral is the highest among the four banks, which indicates a higher risk of liquidity issues if repo creditors become concerned about the bank's solvency. In such a scenario, creditors may choose not to renew their positions, forcing the bank to seek alternative means to raise cash quickly. This could lead to a fire sale of assets, which would not only result in low prices but also potentially lower the market valuation of unsold securities, thereby reducing the amount of cash that could be raised through repurchase agreements collateralized by those securities. The reliance on short-term repo financing makes Bank Q the most susceptible to a liquidity crisis among the A-rated broker-dealer banks listed.