$(ii)$ The $+ M$ effect of $- OCH _{3}$ group increases the basic strength of the following compound. $+ M$ effect of $- OCH _{3}$ is greater than $+ I$ effect of $- CH _{3}$
$(iii)$ Among the given options, the following compound is the most basic as the $- NH _{2}$ group does not involve in the resonance.
$(iv)$ Among the given options, the following compound is the least basic as - $NH _{2}$ group is involved in the resonance.
Thus, the correct order of basic strength is
$iii > ii > i > iv$
$(i)$મિથાઇલ એમાઇન $(ii)$ ફોસ્જીન
$(iii)$ફોસ્ફિન $(iv)$ ડાયમિથાઇલ એમાઇન
$(i)$ મિથાઇલએમાઈન $(ii)$ ફોસ્જિન
$(iii)$ ફોસ્ફિન $(iv)$ ડાયમિથાઇલએમાઈન