Regarding your answer to second question. I was not saying i am using brain wallet. Please read again.
I fully understood you.
I meant i generate a bitcoin private key using secure wallet say for example mycellium wallet which is completely random key BUT the private key that i got now is 100% a SHA256 hash of some random 'text'. so that text might be a 'word' from the dictionary. There's a chance for that. This is what i meant to ask.
There's a chance of that, but that's almost impossible.
If you know that any bitcoin address can be generated by 2^96 private keys on average, you may worry even more. But as I said in my previous post, a bitcoin private key provides enough security and there's nothing to worry about.
One last question. Is it more secure to generate a 24 word seed using dice/coins (manually) OR using CSPRNG present is software like electrum etc ? Which is more secure?