To determine the length of the hypotenuse in the second triangle, we start by noting that both triangles are 45-45-90 triangles. In a 45-45-90 triangle, the sides opposite the 45-degree angles are equal, and the hypotenuse is \( l\sqrt{2} \), where \( l \) is the length of either leg.
For the second triangle:
- The side opposite the 45-degree angle is given as 14. This side is \( l = 14 \).
- Therefore, according to the properties of a 45-45-90 triangle, the hypotenuse \( h \) can be calculated as follows: \[ h = l\sqrt{2} = 14\sqrt{2}. \]
Now, we can cross-reference this calculation with the answer choices provided:
A. The hypotenuse of the second triangle has length \( 7\sqrt{2} \) — This is incorrect. B. The hypotenuse of the second triangle has length \( 14\sqrt{2} \) — This is correct. C. The hypotenuse of the second triangle has length \( 7 \) — This is incorrect. D. The hypotenuse of the second triangle has length \( 14 \) — This is incorrect.
Thus, the length of the hypotenuse in the second triangle is \( \boxed{14\sqrt{2}} \).