Let's analyze each statement regarding the impact of industrialisation.
I. It created employment opportunities in urban areas. This is correct. The growth of factories and industries in cities created a high demand for labor, leading to job creation in urban centers.
II. It led to significant environmental pollution. This is correct. Industrial processes, increased use of fossil fuels, and urban concentration led to widespread air, water, and soil pollution.
III. It decreased the population of urban areas. This is incorrect. Industrialisation caused a massive wave of migration from rural areas to cities in search of jobs, which dramatically increased the population of urban areas.
IV. It made rural agriculture obsolete. This is incorrect. While industrialisation shifted the economic focus and reduced agriculture's share of the total economy, agriculture itself did not become obsolete. It remained (and still is) essential for food production.
The only correct statements are I and II.