In the Bitmap, I bit is required to store the information about the block. If the block is in use then its set as 1 else it set as 0.
Given that, Total Memory = 1.3 GB = (1.3*2^27) bytes
Block size = 512 Byte = (2^9) bytes
Number of Block = (1.3*(2^27))/(2^9) = (1.3*(2^18))
We need (1.3*(2^18)) bit to store all the information about bitmap,
Hence size of Bitmap = (1.3*(2^18)) bit = 1.3*256 KB = 332.8 KB