Final answer:
The number of seconds in a 24-hour day is 8.64 x 10^4 in scientific notation.
Step-by-step explanation:
The number of seconds in a 24-hour day can be calculated by multiplying the number of hours in a day (24) by the number of minutes in an hour (60) and then by the number of seconds in a minute (60).
24 hours/day x 60 minutes/hour x 60 seconds/minute = 86,400 seconds/day.
Therefore, the correct answer is a) 8.64 x 10^4 because 86,400 can be expressed in scientific notation as 8.64 x 10^4.