Explanation:

Post-Independence India: Important events

• Railway network nationalisation: Railways network was nationalised in 1951 and was initially divided into three zones. Indian Railways is now one of the world’s largest railway networks comprising 119,630 km of tracks and 7,216 stations.
• Asia’s fi rst nuclear reactor: India designed and built Asia’s fi rst nuclear reactor Apsara nuclear reactor on August 4, 1956.
• Shimla Agreement: India and Pakistan signed the pact in 1972 “to settle their differences by peaceful means through bilateral negotiations”.
• First Indian satellite made: India designed first space satellite in 1975, named it after astronomer Aryabhata.