Step 1: Set up the players and the game format.
Rishi and Swathi are in Class 5; Pavan and Tanvi are in Class 4. Rishi and Pavan are boys; Swathi and Tanvi are girls. Four students play three games total, and a player who loses a game is out for good. This is a knockout ladder: whoever wins the third game is the only student left who has never lost.
Step 2: Use clue (i) to fix Game 1.
Clue (i) says Game 1 is the only game between two students of the same class. Only two same-class pairs exist: (Rishi, Swathi) from Class 5, or (Pavan, Tanvi) from Class 4. So Game 1 must be one of these two pairs.
Step 3: Test Game 1 = Rishi vs Swathi.
Say Rishi beats Swathi in Game 1. Swathi is out. The remaining three players are Rishi, Pavan, and Tanvi. Game 2 must now pair Rishi with either Pavan or Tanvi, since a second same-class game is not allowed by clue (i).
Step 4: Apply clue (ii) to fix who wins Game 2.
Clue (ii) says Class 5 wins more games than Class 4 out of 3 games, so Class 5 must win at least 2 of the 3 games. Game 1 is already a Class 5 win (Rishi). If Rishi lost Game 2 to a Class 4 player, that Class 4 winner would then face the last remaining Class 4 student in Game 3, a Class4-vs-Class4 game, which guarantees a second Class 4 win. That would give Class 4 two wins and Class 5 only one, breaking clue (ii). So Rishi must win Game 2 as well.
Step 5: Work out Game 3 using clue (iii).
Clue (iii) says boys win two games and girls win one game overall. Game 1 (Rishi) and Game 2 (Rishi) are both boy wins already, so boys already have 2 wins. That means Game 3 must be a girl's win: a girl must beat Rishi in Game 3. Since Rishi already played one of Pavan or Tanvi in Game 2, the only student left for Game 3 is the other Class 4 student, and she must be the girl, Tanvi. So Game 2 was Rishi vs Pavan (Rishi wins), and Game 3 is Rishi vs Tanvi, with Tanvi winning.
Step 6: Check the class win count.
Class 5 wins Game 1 and Game 2 (2 wins), Class 4 (Tanvi) wins Game 3 (1 win), so Class 5 (2) beats Class 4 (1), matching clue (ii). Boys win Game 1 and Game 2 (2 wins), the girl Tanvi wins Game 3 (1 win), matching clue (iii) too.
Final Answer:
Swathi lost Game 1, Pavan lost Game 2, and Rishi lost Game 3. Only Tanvi, who entered the ladder in Game 3 and won it, never lost a single game.
\[ \boxed{\text{Tanvi}} \]