#### Answer

$9.04 \times 10^{-4}$

#### Work Step by Step

RECALL:
In the scientific notation $a \times 10^n$, the value of $a$ is greater than or equal to 1 but less than 10, while $n$ is an integer.
Thus, to write $0.000904$ in scientific notation, do the following steps:
(1) Move the decimal point 4 places to the right to get $9.04$.
(2) To retain the original value, multiply $10^{-4}$ to the result in step (1).
Therefore,
$0.000904=9.04 \times 10^{-4}$