2. Divide the sequence $2,6,10,14, \cdots$ into groups in order, the first group has 2 terms $(2,6)$, the second group has 6 terms $(10,14, \cdots, 30)$, $\cdots$ the $k$-th group has $4 k-2$ terms. Then 1994 belongs to the $\qquad$ group.
2.16
1994 is the 499th term. The first $k$ groups have a total of $2+6+\cdots+(4 k-2)=2 k^{2}$ terms. From $2 k^{2}<499$, we have $k \leqslant 15$. Therefore, 1994 is in the 16th group.