"Psephology" comes from the Greek word "psephos," meaning pebble, since ancient Greek citizens used pebbles to cast their votes. The question tests what the term means today.
Since the word's Greek root and its modern academic use both point to elections, the correct answer is Statistical study of elections, voting, etc..
Another way to answer this is to sort each option into the broader academic discipline it belongs to, then see which discipline actually matches the word "psephology."
Since psephology was specifically coined within political science to describe the statistical analysis of elections, only the first option lines up with the correct discipline.
Therefore, the correct answer is Statistical study of elections, voting, etc..