What if my transaction is not picked by the miners and what is the criteria for miners to pick? How can I rely on blockchain to settle/do fund transfer if it is not getting picked?
You are at the mercy of miners to pick your transaction if you do not try to mine it yourself (which currently would require a substantial investment). Typically, miners will maximize the fee rate (satoshis/kB) for the block they are mining. This means you need to make sure you have a competitive fee based on the size of your tx in bytes.
Are block chains closed distributed networks? I mean, does each company runs its own blockchain. Do I need to register multiple blockchains and pay fees.
Blockchains were created to avoid the need for centralized servers or control. It is a way to establish consensus on a distributed network which is open to the public, which is how Bitcoin was designed. Closed blockchains do exist, however, in various forms such as completely centralized or as federated networks.
To do fund transfer via blockchain,do I need to publish my account balance in public ledger?If yes then where is confidentiality...
Every transaction is available for anyone to validate, this is important in order to prevent double spending. The information that is public only includes your public key, transaction value, and signature(s). If nobody knows you own the public key or address associated with a transaction, then you can remain anonymous, but transactions can be traced back to previously used addresses. There are various methods to maintain privacy such as using different addresses for each transaction. Coinjoin is another example, which allows you, for example, to pool your transaction outputs with others in a single transaction to obfuscate which funds were sent where.
