Explanation:

To identify which unit approximately equals one billion bytes, we refer to the standard conversions of digital storage units. We know that: $1 \text{ Kilobyte (KB)} = 1024 \text{ bytes}$. $1 \text{ Megabyte (MB)} = 1024 \text{ KB} = 1024 \times 1024 \text{ bytes} \approx 1 \text{ million bytes}$. $1 \text{ Gigabyte (GB)} = 1024 \text{ MB} = 1024 \times 1024 \times 1024 \text{ bytes} \approx 1.07 \times 10^9 \text{ bytes}$, which is approximately $1 \text{ billion bytes}$. $1 \text{ Terabyte (TB)} = 1024 \text{ GB} \approx 1 \text{ trillion bytes}$. A Bit is the smallest unit, much smaller than a byte. Therefore, (c) Gigabyte is approximately one billion bytes. Options (a) Kilobyte and (d) Megabyte are too small, representing thousands and millions of bytes respectively. Option (b) Bit is the fundamental binary unit, far too small. Option (e) 'None of these' is incorrect as Gigabyte fits the description.