Express 1.09: Converting Decimal to Different Number Forms

To solve the problem of converting the decimal $1.09$ into a mixed number, we proceed with the following steps:

• Step 1: Identify that the whole number part is $1$.
• Step 2: Convert the decimal part $0.09$ to a fraction. As the digit 9 is in the hundredth place, $0.09$ is equivalent to $\frac{9}{100}$.
• Step 3: Combine the whole number and fractional parts to form the mixed number: $1 \frac{9}{100}$.

Consequently, by converting $1.09$ into a mixed number, we obtain the result: $1\frac{9}{100}$.

Among the provided choices, the correct answer is:

$1\frac{9}{100}$