(i) NFA is more powerful than DFA but DFA is more efficient than NFA.
This is False, Power of NFA and DFA is same.
(ii) NFA will respond for only valid inputs and no need to respond for invalid inputs.
This is true, NFA go final states only for valid i/p's.
(iii) There is no concept of dead states and complement in NFA.
This is true, There is no concept of Dead State, because NFA nothing says about invalid i/p's, and complement also not valid for NFA
(iv) NFA is a parallel computing system where we can run multiple threads concurrently.
This is true, NFA uses parallel Computing System, while accepting a string, if any path lead to termination in Final State, then it stops all other computing, simply says " String is Valid "