The time interval between two successive non when sun passes through zenith point (meridian) is known as
A. Sidereal day
B. Moon solar day
C. Solar year
D. Lunar month

Hint: Mean solar day is the time interval between two successive noon when the sun passes through the zenith point (meridian).

Complete step by step answer:
Mean solar day is the internal between successive transits of a given meridian of longitude by the mean sun.
The confusion wasn’t resolved for good until 1884 when at an international time conference in Washington DC, replaced the old-fashioned solar day with the man solar day-a legal fiction in which the daily fluctuations are averaged out, enabling us to enjoy the blessings of a uniform 24-hour day all year long.
A mean solar day is 24 hours. An apparent day may be between 20 to 30 seconds shorter or longer than this due to the effects above but obviously for the sake of time keeping, it is sensible to use on average.
The mean sun is an imaginary sun which matches a mean solar day exactly.

Note: Universal time is based on the motion of one imagmany ‘meon sun’. Sidereal day is the time interval between two successive transits of a distant star through the zenith point (meridian).
By drawing an appropriate diagram showing the earth’s spin and orbital motion, it shows that mean solar day is 4 minutes longer than the sidereal day. In other words, distant stars would rise 4 minutes early every successive day.