$^0$gc resources
$^{1:n}$Complete Chemistry for Cambridge IGCSE, page number $n$
$^4$https://www.youtube.com/watch?v=lQ6FBA1HM3s&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGr
$^5$https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Electrochemistry/Redox_Chemistry/Half-Reactions