Step 1: EU Expansion.
Croatia acceded to the European Union as its 28\textsuperscript{th} member on July 1, 2013, after extensive negotiations and reforms.
Step 2: Analysis of options.
- (1) 2010: Incorrect. Croatia's EU entry was not in 2010.
- (2) 2011: Incorrect. 2011 is not the year of Croatia's EU accession.
- (3) 2013: Correct. Croatia joined the EU in 2013, becoming its 28\textsuperscript{th} member.
- (4) 2014: Incorrect. Croatia's EU membership began in 2013, not 2014.
Step 3: Conclusion.
Therefore, the correct answer is (3) 2013, which marks Croatia's entry into the EU as its 28\textsuperscript{th} member.