Answer
$r=10^{d}$, see explanations.
Work Step by Step
Step 1. Given $a_n$ as an arithmetic sequence with common difference $d$, we have $a_{n+1}-a_n=d$
Step 2. Let $b_n=10^{a_n}$ be a new sequence, we have $\frac{b_{n+1}}{b_n}=\frac{10^{a_{n+1}}}{10^{a_n}}=10^{a_{n+1}-a_n}=10^{d}$
Step 3. As $d$ is a constant, we can identify that $b_n$ is a geometric sequence with a common ratio of $r=10^{d}$.
