The correct answer is Option 4: Cotton, silk, saltpetre and opium.

During the middle of the 18th century, the English East India Company (EIC) was one of the major players in the trade of Indian goods. Bengal, in particular, was a significant source of export for the EIC. The staple commodities of export by the EIC from Bengal during this period were cotton, silk, saltpetre and opium.

Cotton was one of the most important commodities exported by the EIC from Bengal. It was in high demand in Europe, where it was used to produce textiles. Bengal was a major producer of cotton and had a comparative advantage in producing fine muslin, which was highly prized in Europe.

Silk was another important commodity exported by the EIC from Bengal. The region had a long tradition of silk production and was renowned for its high-quality silk. The EIC exported both raw silk and silk fabrics, which were in high demand in Europe.

Saltpetre, also known as potassium nitrate, was a key ingredient in the production of gunpowder. Bengal was a major source of saltpetre, and the EIC exported large quantities of the commodity to Europe.

Opium was another important commodity exported by the EIC from Bengal. The EIC had a monopoly on the opium trade in India and exported large quantities of opium to China, where it was in high demand. The opium trade was a controversial issue during this period and was one of the main factors that led to the Opium Wars between Britain and China in the 19th century.

In conclusion, during the middle of the 18th century, the staple commodities of export by the English East India Company from Bengal were cotton, silk, saltpetre, and opium. These commodities were in high demand in Europe and China and played a significant role in the trade between India and these regions.