To determine how many of the given pairs are correctly matched, we need to evaluate each pair based on their actual purpose within international financial mechanisms:

1. Extended Fund Facility (EFF) : For structural balance of payments problems.
   • The EFF is designed to provide assistance to countries experiencing serious balance of payments problems because of structural issues. It allows them to implement comprehensive programs that include policies necessary for correcting these structural imbalances.
   • Verdict: Correctly matched.
2. Rapid Credit Facility (RCF) : Quick and concessional lending for high-income countries.
   • The RCF provides rapid financial assistance to low-income countries with critical and urgent balance of payments needs, without the need for a full-fledged program or review by the IMF board.
   • It is targeted at low-income countries, not high-income countries.
   • Verdict: Incorrectly matched.
3. Resilience and Sustainability Facility (RSF) : Short-term liquidity line.
   • The RSF is aimed at providing longer-term financing to support countries in building resilience to climate change, pandemics, and related challenges.
   • It does not serve as a short-term liquidity line.
   • Verdict: Incorrectly matched.

Based on the analysis above, only Pair 1 is correctly matched. Therefore, the correct answer is: