Assertion: Haryana has the highest density of national highways (km per 100 sq km) in India.
Reason (R): Haryana's location adjoining Delhi and in the NCR makes it a crucial transit state.

Correct option is A

The correct answer is The correct answer is (a) Both A and R are true, and R is the correct explanation of A
Explanation:
. Assertion (a) is true. Haryana does boast one of the highest densities of National Highways (length per unit area) among all Indian states, primarily due to its strategic location and well-developed road network connecting it to the capital and neighboring states.
. Reason (R) is true. Haryana completely surrounds the National Capital Territory (NCT) of Delhi on three sides (North, West, South) and is part of the National Capital Region (NCR). This makes it a crucial transit corridor for all road traffic moving in and out of Delhi towards Punjab, Rajasthan, Uttar Pradesh, and beyond.
. Reason (R) is the correct explanation of Assertion (a). The geographical location and role as a transit state (R) necessitates a high density of highways (a), providing the logical reason for the assertion.
Information Booster:
. Good road infrastructure in Haryana has been a key driver for its rapid industrialization and economic growth.
. States like Kerala also have very high road density (including state highways/major district roads), but specifically for  National Highways density, Haryana is typically at the top.
. Major national highways like NH-44 (Srinagar-Kanyakumari highway, passing through Haryana) contribute significantly to this density.