A regular language L is accepted by a non-deterministic finite automaton (NFA) with n states. Which of the following statement(s) is/are FALSE?
Topic-wise GATE CS PYQs with verified steps
GATE CSE 2025 Set 1 · Q28
Time
Select all that applyOne or more correct
Solution
Official answer: D) Every DFA that accepts L has > 2n states.
Regular Expressions and Finite AutomataLet an NFA have states accepting language .
Option (A): *" may have an accepting NFA with states."*
This is TRUE. If the given -state NFA contains redundant or unreachable states, there may exist an equivalent NFA with fewer states.
Option (B): *" may have an accepting DFA with states."*
This is TRUE. An NFA with non-minimal states can be equivalent to a minimal DFA having strictly fewer than states (e.g., an NFA with redundant states accepting ).
Option (C): *"There exists a DFA with states that accepts ."*
This is TRUE. By the subset (powerset) construction, every NFA with states can be converted into an equivalent DFA with at most states.
Option (D): *"Every DFA that accepts has states."*
This is FALSE. Since the subset construction always yields an equivalent DFA with at most states, it is impossible for all equivalent DFAs to require more than states.
Since the question asks for the statement(s) that is/are FALSE, the correct option is (D).
Try the question first, then check your work.
Examiner trap
Recall the subset construction theorem for converting an NFA to a DFA, and consider whether an NFA or DFA given for a language is necessarily minimal.
This Regular Expressions and Finite Automata previous year question is Q28 of the GATE CSE 2025 Set 1 paper. Find more GATE CSE PYQs on Regular Expressions and Finite Automata in Theory of Computation, or browse all GATE CSE PYQs.
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Regular Expressions and Finite Automata has 41 GATE CSE PYQs across 24 papers from 2011 to 2026. 2 of them are 1-mark MSQs like this one, and GATE CSE 2025 Set 1 has 2.
How GATE tests Regular Expressions and Finite AutomataIndependent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.