To calculate how long it takes for Earth to rotate on its axis 7 times, we need to know the time it takes for one complete rotation, which is a day. Therefore, if Earth rotates once in 24 hours, to rotate 7 times, we can multiply the number of rotations by the time for one rotation:
1 rotation = 24 hours
7 rotations = 7 * 24 hours = 168 hours
So, it takes 168 hours for Earth to rotate on its axis 7 times.
a) one day is equivalent to 24 hours, which is the time for one complete rotation of Earth, not 7 rotations. So, this option is incorrect.
b) one week is equal to 7 days, which is more than the time it takes for Earth to rotate 7 times. Therefore, this option is incorrect.
c) one month can vary in days, but on average, a month is around 30 days. This is also more than the time needed for Earth to rotate 7 times, so this option is incorrect.
d) one year is equal to 365 (or 366 in a leap year) days, which is significantly more than the time required for Earth to rotate 7 times. Hence, this option is incorrect as well.
Therefore, the correct answer is: a) one day
