The initial proposal and subsequent release of the First Five-Year Plan in December 1951 generated considerable enthusiasm throughout the country. Individuals from diverse backgrounds, including academics, journalists, government officials, private sector employees, industrialists, farmers, and politicians, actively engaged in extensive discussions and debates surrounding the plan. The enthusiasm for planning reached its zenith with the commencement of the Second Five-Year Plan in 1956 and persisted to some extent until the Third Five-Year Plan in 1961. The implementation of the Fourth Plan was scheduled to commence in 1966.

Assertion: K.N. Raj argued that India should ‘hasten slowly’ for the first two decades in order to get the country's economy out of poverty.
Reason: The First Five Year Plan addressed, mainly, the agrarian sector including investment in dams and irrigation.

Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

The draft of the First Five-Year Plan and then the actual Plan Document, released in December 1951, generated a lot of excitement in the country.
The First Five-Year Plan (1951–1956) sought to get the country’s economy out of the cycle of poverty.
K.N. Raj, a young economist involved in drafting the plan, argued that India should ‘hasten slowly’ for the first two decades as a fast rate of development might endanger democracy.
The First Five Year Plan addressed, mainly, the agrarian sector including investment in dams and irrigation.
The agricultural sector was hit hardest by Partition and needed urgent attention.
Huge allocations were made for large-scale projects like the Bhakhra Nangal Dam.
The Plan identified the pattern of land distribution in the country as the principal obstacle to agricultural growth.
It focused on land reforms as the key to the country’s development.