The question asks for the immediate step taken in 1991 to tackle India's balance of payments (BoP) crisis, the situation where a country cannot pay for its imports and external obligations.

By mid-1991 India's foreign exchange reserves had fallen to critically low levels, barely enough to cover about two to three weeks of imports, and the country was on the brink of defaulting on its external payments.

To restore external stability the government needed to make Indian exports cheaper and more competitive abroad while making imports costlier, thereby narrowing the yawning trade deficit.

Accordingly, the Reserve Bank of India, acting for the government, devalued the rupee sharply against major foreign currencies in two steps on 1 and 3 July 1991, a cumulative fall of roughly 18-19 per cent against the US dollar.

This devaluation boosted export earnings and discouraged imports, and it was quickly followed by other emergency measures such as pledging gold reserves and, soon after, the wider 1991 liberalisation and structural-reform programme.

Increasing import restrictions would have hurt industry and invited retaliation, revaluing the rupee (making it dearer) would have worsened the deficit, and imposing a fixed exchange rate was not the immediate remedy adopted, so those options are incorrect.

Hence, the immediate measure taken in 1991 was the devaluation of the rupee against foreign currencies.