One light year is equal to:
\[\begin{align}
  & A)3.2par\sec \\
 & B)3.26Km \\
 & C)3.26AU \\
 & D)\dfrac{1}{3.26}par\sec \\
\end{align}\]

Hint: A unit of length which is used to measure the large distances of celestial bodies outside the solar system is known as parsec. It is obtained by using trigonometry and parallax. For space objects light-years are used to describe their distance. The distance that light travels in one Earth year is called a light year.

Complete answer:
A light year is equal to \[\dfrac{1}{3.26}par\sec \].
One parsec is the distance to an object in space whose parallax angle is one arc second. A parsec is a unit of distance which is equal to about 19 trillion miles (more than 30 trillion km) and it is used to figure out the size of the universe. Astronomers use triangulation to find the distance to a nearby star.

In this image, the line from that star to the sun and the line from the star to Earth can be said to represent a radius measure. One radian (radius measured along the circle’s circumference) is equal to 206,265 arc seconds or 57.2958 degrees) Hence, a star with a parallax of one arc second must be 206,265 times the Earth-sun distance away. These angles are too small for measuring in degrees. That’s why parallax angles are measured in arc seconds. Therefore, one parsec is the distance to an object in space whose parallax angle is one arc second. One parsec is approximately equal to 19 trillion miles (30 trillion km). The nearest star to the sun is just over one parsec from us.

Note:
The closest spiral galaxy to us is nearly 800 kilo parsecs away. One thousand parsecs equals a kilo parsec. At larger scales, astronomers use giga parsecs and megaparsecs, which are one billion and one million parsecs respectively. These are now being used for the largest structures in existence.