Rewrite the first term as a square root too: 1 = √1. Now the series reads √1, √2, √3, ?, √5 — so the pattern is clearly √1, √2, √3, √4, √5 (square roots of consecutive counting numbers). The 4th term should be √4 (which equals 2), but instead the series shows plain '4'. So '4' is the term that doesn't fit the pattern, option (2).