Bank Q is most vulnerable to a liquidity crisis because it has the largest dependence on short-term repo financing, as indicated by the highest percentage of its assets pledged as collateral among the four banks. A liquidity crisis could occur if repo creditors become concerned about the bank's solvency and decide not to renew their positions. This could lead to the bank being unable to raise sufficient cash quickly through other means, potentially forcing it to sell assets at a discount in a "fire sale." The proportion of assets covered by repos serves as a signal of liquidity risk, and in the event of a fire sale, low prices could also reduce the market valuation of unsold securities, further limiting the bank's ability to raise cash through repurchase agreements collateralized by those securities.