Naked Pairs
Sudoku Solving Technique
The Naked Pairs technique is one of the most common and powerful tools for cracking medium and hard Sudoku puzzles. It relies heavily on you filling out pencil marks (candidates) for empty cells.
How it Works
If you find two cells within the same group (a row, a column, or a 3x3 block) that contain exactly the same two candidates—and no other candidates—you have found a Naked Pair.
Because those two specific cells can only be filled by those two specific numbers, it is mathematically impossible for those numbers to appear anywhere else in that group. Therefore, you can safely erase those two numbers from the candidate lists of every other empty cell in that group.
Example
Imagine a 3x3 block where two cells only have the pencil marks "3" and "7". You don't know which cell is the 3 and which is the 7 yet, but you know for a fact that they occupy those two cells. If another cell in that same 3x3 block has the pencil marks "3, 7, 9", you can safely erase the 3 and the 7, leaving "9" as the only possible answer for that cell!