did cities like dacca and murshidabad lose their importance in the mid 19th century

The following points may help you:

a. Murshidabad lost its importance in the 19th century, primarily because of advent of British machine made goods in the country.
b. As a result its hand made industry, silk, scarves, sarees received a huge blow.
c. Besides that Murshidabad was also the political seat of the Nawab of Bengal, after the Nawab was defeated in the Battle of Plassey, the capital of Bengal was shifted to Calcutta,
d. Dacca continued to hold importance with the British establishing Cantonment, civic water supply, railway lines.