We know that for the first excited state, n = 2. We use Bohr's quantization rule for angular momentum, which states that $m v_n r_n = n \hbar$, where $\hbar = \frac{h}{2\pi}$ and $r_n = 0.529 n^2 \times 10^{-10} m$. So, $r_2 = 0.529 \times 2^2 \times 10^{-10} m =
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