Assertion: The condition of the Indian part of Bengal City like the excessive vegetation, the dirty tanks, poor drainage, etc worried Lord Wellesley.
Reason:  The Britishers believed at the time that poisonous gases from marshlands and pools of stagnant water were the cause of most diseases.

Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

The correct answer is Option 1 - Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Assertion: The condition of the Indian part of Bengal City like the excessive vegetation, the dirty tanks, poor drainage, etc worried Lord Wellesley.
Reason:  The Britishers believed at the time that poisonous gases from marshlands and pools of stagnant water were the cause of most diseases.

The history of town planning in Calcutta did not end with the building of Fort William and the Maidan. In 1798, Lord Wellesley became the Governor General. He built a massive palace, Government House, for himself in Calcutta. He became concerned about the condition of the Indian part of the city- the crowding, the excessive vegetation, the dirty tanks, the smells and poor drainage. These conditions worried the British because they believed at the time that poisonous gases from marshlands and pools of stagnant water were the cause of most diseases. The tropical climate was itself seen as unhealthy and enervating.

More information:

The 18th-19th century was a period when Europeans held strong beliefs about miasma theory. This theory associated diseases with "bad air" emanating from swamps, decaying matter, and stagnant water.

The assertion and reason both seem to accurately reflect the concerns of the British during the 18th-19th century in Bengal, India. The British colonial administration indeed found the environmental conditions, such as excessive vegetation and stagnant water, troubling. They attributed many diseases to what they termed "miasma," or poisonous gases emanating from marshlands and stagnant water bodies. This theory led them to prioritize sanitation and urban planning reforms aimed at improving public health in cities like Calcutta (now Kolkata). Thus, both the assertion and reason are correct and related.