Kharagpur has the longest platform in the world and in India.
The 2nd longest platform in India is said to be on Sonepur railway station, Sonepur, Bihar.
The lengths of these two are,
1.Kharagpur, West Bengal, India: 1,072 m (3,517 ft)
2.Sonepur...
more... railway station, Sonepur, Bihar, India: 738 m (2,421 ft)
But, Daund Jn.(Daund, Maharashtra) has platform no. 1 & 2 combined with an approximate length of 901 m.
The image from Google Maps shows the approximate length of Daund Jn. platform 1 & 2 combined.