:To Ragib, It seems to me that there is no need to go to the Constitution and look for references to "official languages."  Those are already discussed (as mentioned by K-H above) on the "Official Language Policy" page of the Government of India.  The page is pretty complete and its sidebars include: 

 :*Official Language Policy 
 :*Constitutional Provisions 
 :*President's Orders 
 :*Official Languages Act 
 :*Official Languages Resolution 
 :*Official Language Rules 
 :*Chronology of Events with Reference to the Official Language of the Union 

 :Going to the constitution (and its amendments) to look for exact and accurate quotations invariably leads to questions of meaning, intent, and original intent—all trapdoors to a bottomless quest.  In addition, both Britannica and Encarta (especially the former) are widely respected tertiary sources and they agree on the question of "official languages" for India.  That needs to be taken seriously.   I am happy to look at secondary sources all well, but to go to the primary sources and parse intent is problematic.