The correct spelling of the law that states "the rate of diffusion of a gas is inversely proportional to the square root of its molecular weight" is "Graham's law," named after Scottish chemist Thomas Graham. It is often mistakenly spelled as "Semons law," which is incorrect. The pronunciation of the correct term, "Graham's law," is /ˈɡreɪ.əmz lɔː/. The incorrect spelling, "Semons law," is pronounced /ˈsiːmənz lɔː/, but should not be used. It is important to use correct spellings and pronunciations in academic and professional settings to avoid confusion and ensure clarity of communication.