To express \( 8.64 \times 10^4 \) seconds in standard form, you need to calculate the value.
Calculating \( 8.64 \times 10^4 \):
\[ 8.64 \times 10^4 = 8.64 \times 100,000 = 86,400 \]
So, \( 8.64 \times 10^4 \) seconds is equivalent to 86,400 seconds.
Therefore, the correct answer is:
C. 86,400 seconds