Long-term solvency of a firm can be judged by using Leverage/Capital Structure Ratios (e.g., Debt-Equity Ratio, Interest Coverage Ratio).
Source: Chapter 10, Leverage/Capital Structure Ratios
The examiner expects you to name the ratio category — Leverage or Capital Structure Ratios — not individual ratios. Mentioning one example is a good habit for a 1-mark answer but not strictly required. Avoid writing about liquidity ratios; those measure short-term solvency.