1.)I checked the electrum code and it also uses RNG that just picks a random number between 1 and 2^256 so therotically RNG can a pick a 10 digit number too? or am i missing something here?
That's true only in theory. The probability of getting a 10 digit number is almost zero.
2.) Second question i have is. We all know how SHA256 can be used to convert any 'text' to a hash which is a valid private key right a.k.a brain wallets.
It's not recommended to use brain wallets. It's recommended to generate a random private key.
So my question is what if my wallet generate a key which is secure but what if that key is SHA256 hash of some 'poor dictionary word'?
No. There is no risk. What you worry about can happen only in theory. A private key generated properly provides enough security.
Regarding your answer to second question. I was not saying i am using brain wallet. Please read again.
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.