Number of cylinders = Number of tracks on each surface, so I is true
Block size is always a multiple of sector size which is $512B$ for ex, $1024B, 1536B, 2048B$ are valid block size
But $51200B$ is not a valid block size, because
if we calculate size of sector= $50*512= 25600B$ and block size cannot exceed size of sector, so II is false
Hence Option C) is correct