Q1: Which of the following is a unit of time ?

ANS:D - none of these

Among the options provided, none of these is a unit of time. Explanation:

1. Barn: A barn is a unit of area used in particle physics to describe the cross-sectional area of atomic nuclei and other subatomic particles. It is not a unit of time.
2. Light Year: A light year is a unit of distance, not time. It represents the distance that light travels in one year in a vacuum. Light years are commonly used to measure vast distances in astronomy.
3. Angstrom: An angstrom is a unit of length used to measure very small distances, particularly in the realm of atomic and molecular scales. It is equal to 0.1 nanometers. Angstroms are not used to measure time.