$\ce{HI/P}$ is used for reduction of alcohols, aldehydes, ketones and acids to alkanes. As for alkyl halides, I have read that only alkyl iodides are reduced, whereas other alkyl halides do not: $$\ce{CH3CH2I ->[Red P][\pu{1 eq.}~HI] C2H6 + I2}\tag{R1}$$ But I have also been taught that all alkyl...