ANS = 698 .
Index is being built on attribute “ANum” which is Candidate Key, but Given that file is Sorted on Primary Key “Roll No”.
This indicates that The Index must a Secondary Index, (data records not being physically ordered as per the index making a dense record necessary) so “THERE SHOULD EXIST AN INDEX RECORD FOR EVERY RECORD of Original ‘Student Table’ ”.
=> Also this Line: “Assume that Records of data file and index file are not split across disc blocks”.
This indicates UNSPANNED STRATEGY.
With This Knowledge, let’s see the Data given.
→ Record Size in Index $= 12 + 7 = 19 \text{ B}$ (‘ANum’ key size + Record pointer Size), and Block Size $= 4096 \text{ B}$
→ So number of Index records in 1 Block $= \left \lfloor \frac{4096}{19} \right \rfloor= 215$ records in 1 block (Remember again, unspanned strategy).
→ So number of blocks in the Index file $= \dfrac{\text{Total Number of records}}{\text{Records per block}} = \left \lceil \dfrac{1,50,000}{215}\right \rceil = 698.$
(Recall that this is Secondary Index)