Which of the following is a Gaussian integer (element of Z[i]\mathbb{Z}[i]Z[i])?
2.5+3i2.5 + 3i2.5+3i
3+2i3 + \sqrt{2}i3+2i
4−7i4 - 7i4−7i
π+2i\pi + 2iπ+2i