To convert an NFA with 6 states (excluding the initial state) into a DFA, we need to consider the power set construction method. This method involves creating new states in the DFA that represent subsets of states from the NFA.

To determine the maximum possible number of states for the DFA, we need to calculate the number of subsets of 6 states. The formula for calculating the number of subsets of a set with n elements is 2^n. In this case, we have 6 states, so the number of subsets is 2^6 = 64.

However, we need to consider that the initial state of the DFA is always included. Therefore, the maximum number of states for the DFA is 64 - 1 = 63.

But wait! We also need to account for the fact that some of these subsets may be unreachable or equivalent. Unreachable states are those that cannot be reached from the initial state, and equivalent states are those that produce the same behavior (i.e., they have the same transitions and accept the same inputs).

To eliminate unreachable states, we can perform a reachability analysis starting from the initial state. Any states that cannot be reached are not included in the DFA.

To eliminate equivalent states, we can perform an equivalence analysis. This involves comparing the transitions and accepting states of each pair of states. If two states have the same transitions and accept the same inputs, they can be considered equivalent and merged into a single state in the DFA.

Performing reachability and equivalence analysis can reduce the number of states in the DFA. However, it is not possible to determine the exact number of states without analyzing the specific NFA in question.

Therefore, the correct answer is option C) 128, as it represents the maximum possible number of states for the DFA without considering unreachable or equivalent states.