Let the cost of a 2-inch marble be \( x \) dollars. Then the cost of a 1-inch marble will be \( x - 0.30 \) dollars.
Rochelle buys 25 1-inch marbles for $10, so we can set up the following equation:
\[ 25(x - 0.30) = 10 \]
Now, simplify this equation:
\[ 25x - 7.5 = 10 \]
Next, add 7.5 to both sides:
\[ 25x = 17.5 \]
Now, divide both sides by 25 to solve for \( x \):
\[ x = \frac{17.5}{25} = 0.70 \]
Thus, the cost of a 2-inch marble is $0.70.
So, the correct response is \( \text{$0.70} \).