UPSC Civil Services Model Paper 6

Indian Standard Time is calculated on the basis of 82.58° E longitude and is uniform all around the country. ( 5.5 hours ahead of Greenwich Meridian Time ) Hence statement 2 is correct.
Standard Time : A uniform time for places in approximately the same longitude, established in a country or region by law or custom.
International Date Line is also known as the line of demarcation as it separates two consecutive calendar dates.
It is an imaginary longitude located at about 180 degrees east or west from the Greenwich Meridian .
Hence statement 1 is correct.
It is not straight and curves from the normal 180 degrees Meridian at the Bering Strait, Fiji, Tonga, Aleutian Islands, Kiribati Islands, WrangelIs land , etc. to prevent confusion of day and date .
Hence, statement 3 is correct .
The time difference between either side of the international date line is not always 24 hours because of uncertainties due to local time zone variations .
Date changes when one crosses it.
If one crosses the dateline moving east, then one has to subtract a day .
Whereas if one is moving West then one has to add a day .