I tried to send an ERC20 token to 100 addresses at once by the method 'web3.eth.sendRawTransaction(), but only 7~12 transactions succeeded and 88~93 transaction failed. What could the problem be?

Be sure to check the nonces in the transactions. While firing transactions rapidly, due to P2P network delays and our load balancing, some of the returned nonce values will be “behind”. To avoid this, manually increment the nonce.

I want to transfer ETH from an address to another address on ropsten network. but I have no idea that how to use it. So please can you help me for this ?

Please review our docs here for the send raw transaction method, https://infura.io/docs/ethereum/json-rpc/eth_sendRawTransaction