Explanation:

Only statement 3rd is correct.

• Statement 1 is incorrect: One nation one election, also known as simultaneous elections,refers to the practice of holding elections to Lok Sabha, all the state assemblies, and local bodies – municipalities and panchayats, together in phased manner not in single day

• Statement 2 is incorrect: Its implementation require constitutional amendment.

• One nation one election (simultaneous elections):

• ONOErefers to the proposal of holding simultaneous elections for the Lok Sabha and all State Legislative Assemblies in India.

Key Features of One Nation, One Election

• Simultaneous Elections: Lok Sabha and State Legislative Assemblies would have synchronized election schedules.

• Reduced Frequency: Elections would be held once every five years, or earlier if required.

• Single Voter List: A unified electoral roll would simplify the voting process and reduce duplication.

• Uniformity in Electoral Processes: Common logistical and administrative arrangements for elections.

Benefits of One Nation, One Election:

• Administrative Convenience: It reduces the workload on the Election Commission and government machinery by conducting elections less frequently.

• Focus on Governance: Frequent elections disrupt governance due to the Model Code of Conduct. Holding elections together ensures uninterrupted policy implementation.

• Cost Efficiency: Simultaneous elections could significantly reduce the expenditure on election logistics, security, and campaigning. 

• Improved Voter Turnout: Consolidating elections might increase voter participation by simplifying the voting process.

Challenges and Concerns of One Nation, One Election:

• Constitutional Issues: It requires amendments to multiple articles of the Constitution (e.g., Articles 83, 85, 172, 174, 356) to align election schedules.

• Operational Complexity: Managing logistics, security, and the electoral process for simultaneous elections across the nation is a significant challenge.

• Political Feasibility: Synchronizing elections for all states could face resistance from regional parties and stakeholders.

• Risk of Disruptions: A single national election schedule might lead to large-scale disruptions in governance if assemblies or the Lok Sabha are dissolved prematurely.

Hence option 3rd is correct.