The problem of international liquidity is related to the non-availability of

The correct option is dollars and other hard currencies.

Understanding International Liquidity:
International liquidity refers to the aggregate stock of financial resources—such as gold, foreign exchange reserves, and Special Drawing Rights (SDRs)—that are globally accepted for settling international trade transactions and balancing payment deficits between nations.

Why Hard Currencies Matter:
In the global economy, the vast majority of international trade, investments, and debt payments are denominated in major, highly stable currencies known as "hard currencies" (most notably the United States Dollar, Euro, Japanese Yen, and British Pound). Because these currencies are universally accepted and liquid, countries must hold them in reserve to conduct international commerce.

The Core Problem:
The "problem of international liquidity" arises when there is a systemic shortage or non-availability of these globally accepted reserve assets relative to the volume of international trade. When countries, particularly developing nations, cannot obtain enough dollars and other hard currencies, they struggle to finance vital imports or meet foreign debt obligations, leading to balance of payments crises. Thus, the liquidity problem is directly tied to the scarcity of these key currencies.