I want to store one bitcoin in my pendrive and how much free space do I need to store that information?
TL;DR: 32 bytes.
Bitcoins are not pieces of data, Bitcoin is a unit of measure.
To store any amount of Bitcoin in a pendrive you just store a private-key on the pendrive. That is a 256-bit number. It is exactly the same size for 0 Bitcoin, 0.00001 Bitcoin, 1 Bitcoin or for 21,000,000 Bitcoin.
To store the full history, since the beginning of time, of transfers of control of money denominated in Bitcoin, you need about 300GB and growing. But this is public information, you don't need to store it yourself as you can always obtain a copy from other Bitcoin nodes. This data is a journal of transactions called the blockchain.
Of course, you can't really point to any particular place or thing and say Bitcoin are stored there. That isn't really what is happening.
The 32 bytes (256 bits) is the smallest amount of space you will need. If you want to represent that number as printable ASCII or Unicode characters you'll need to choose an encoding scheme like Hex or Base58 etc which will increase the storage requirements.
You can store 21,000,000 Bitcoins in the space needed to store a set of letters and numerals the same length as this example:
For convenience you will most likely install a file system such as FAT on your pen-drive. The file system will have overheads and a minimum allocation unit.
1 bitcoin = 100000000 sats 100 sats = 1 bit
Those "bits" are a completely different thing to the 8 bits in a byte.
In December 2017, BIP-176 also proposed "Bits" be used as a standard term for 100 (one hundred) satoshis or 1/1,000,000 (one one-millionth) of a bitcoin.
That's nothing to do with the units of computer storage.
Just like its nothing to do with the "bits" that horse-riders put into the mouths of horses.
not 100 Satoshi, and you cannot store 8 of these in a byte