UPSC NDA II 2025 General Ability Paper

Concept:A parsec is the distance at which one astronomical unit (A.U.) subtends an angle of one arcsecond. This directly links parsec and A.U. through geometry.Explanation:The definition of parsec implies that $1 \text{ parsec} = \frac{1 \text{ A.U.}}{\tan(1'')}$. Since $\tan(1'') \approx 4.848 \times 10^{-6}$ radians, the reciprocal gives $1 \text{ parsec} \approx 206,\!265 \text{ A.U.}$. Convert this number to scientific notation: $206,\!265 \approx 2.06 \times 10^5$, which rounds to $2 \times 10^5$ for the given options. Thus, one parsec is about $2 \times 10^5$ astronomical units.Answer:C. $2 \times 10^5$ A.U.