$^1$Notes, if it has a ! in it, it is notes from 9th

$^{2(N)}$Complete Chemistry for Cambridge IGCSE, page number N. Link to the book: https://drive.google.com/file/d/1Zp_nuiNRmTyLQsI3adMXf_CpRHP1xDi4/view?usp=sharing

$^3$ https://chem.libretexts.org/Courses/can/intro/04:_Atoms_and_Elements/4.9:_Atomic_Mass:_The_Average_Mass_of_an_Elements_Atoms

$^4$https://byjus.com/question-answer/what-is-percentage-purity/