• question_answer 83)                            Assertion (A): One atomic mass unit is defined as one twelfth of the mass of one carbon-12 atom. Reason (R): Carbon-12 isotope is the most abundant isotope of carbon and has been chosen as standard. (a) Both A and R are true and R is the correct explanation of A.                                                    (b)Both A and R are true but R is not the correct explanation of A. (c) A is true but R is false. (d) Both A and R are false.

(b) $1amu=\frac{1}{12}\times Mass\,of\,one\,{{C}^{12}}atom$ ${{C}^{12}}$ isotope is considered as standard for defining the atomic and molecular mass.