The correct option is 7°30'.
Explanation
The Earth rotates 360° in approximately 24 hours, which implies a rotation of 15° in one hour or 1° in four minutes. To maintain a logical and convenient system of time zones globally, countries adopt standard meridians that allow their standard time to differ from Greenwich Mean Time (GMT) by integral multiples of one hour or half an hour.Detailed Analysis:
- 5°30' is incorrect: 5°30' is not a standard angular unit for time zones. It is often confused with the time difference of Indian Standard Time (IST) from GMT, which is 5 hours and 30 minutes.
- 7°30' is correct: There is a general international agreement to select the Standard Meridian of a country in multiples of 7°30' of longitude. Since 15° corresponds to 1 hour, 7°30' corresponds to exactly 30 minutes. This allows standard times to be expressed as full hours or half-hours relative to GMT. For example, India's Standard Meridian is 82°30' E, which is a multiple of 7°30'.
- 15° is incorrect: While 15° represents a one-hour time difference and is the width of a standard theoretical time zone, the specific rule for selecting a meridian allows for half-hour adjustments, making 7°30' the governing multiple.
- 4° is incorrect: 4° does not correspond to a standard time unit. The number 4 relates to the fact that the Earth takes 4 minutes to rotate 1°.
Key Takeaway:
Standard Meridians are generally selected in multiples of 7°30' of longitude to ensure that the local standard time differs from Greenwich Mean Time by multiples of 30 minutes.