Which one of the following is correct ? The mean distance from the Sun to the Earth is called a/an

The mean distance from the Sun to the Earth is defined as an Astronomical Unit (AU). This unit is a standard measurement in astronomy used to describe distances within our solar system [t1][t3]. The International Astronomical Union (IAU) defines 1 AU as exactly 149,597,870,700 meters, which is approximately 149.6 million kilometers or 93 million miles [t1][t2][t7]. While a Light Year (Option 1) measures the distance light travels in one year (approx. 9.46 trillion km) [c1][c5], and a Parallactic Second or Parsec (Option 2) represents the distance at which 1 AU subtends an angle of one arcsecond [t1][t9], the AU specifically represents the Earth-Sun average distance [t6][t8]. Angstrom (Option 4) is a microscopic unit of length (10^-10 meters) used for atomic scales. Therefore, the AU is the correct term for the mean Earth-Sun distance.

Sources

1. [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 2: The Origin and Evolution of the Earth > The Star Formation > p. 14
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 1: The Universe, The Big Bang Theory, Galaxies & Stellar Evolution > Our Galaxy (The Milky Way) > p. 8