Consider a file currently consisting of $50$ blocks. Assume that the file control block and the index block is already in memory. If a block is added at the end (and the block information to be added is stored in memory), then how many disk $I/O$ operations are required for indexed (single-level) allocation strategy ?
Since file control block and the index block is already in memory we need not fetch them from disc.
We need to copy the new block to be added from disc (1 I/O operation). that's it
Answer will be A