Long term solvency is indicated by:

Debt/Equity Ratio

The correct answer is option 4- Debt/Equity Ratio.

The persons who have advanced money to the business on long-term basis are interested in safety of their periodic payment of interest as well as the repayment of principal amount at the end of the loan period. Solvency ratios are calculated to determine the ability of the business to service its debt in the long run.
The following ratios are normally computed for evaluating solvency of the business:
1. Debt-Equity Ratio; 2. Debt to Capital Employed Ratio; 3. Proprietary Ratio; 4. Total Assets to Debt Ratio; 5. Interest Coverage Ratio.

Debt-Equity Ratio measures the relationship between long-term debt and equity. If debt component of the total long-term funds employed is small, outsiders feel more secure. From security point of view, capital structure with less debt and more equity is considered favourable as it reduces the chances of bankruptcy. Normally, it is considered to be safe if debt equity ratio is 2:1.