Explanation

(c)
According to Fajan’s rule smaller anion is polarised to lesser extent than the larger anion.
$\therefore$ compound having smaller anion has more ionic character.
$\therefore$ Higher melting
Since, the size of $F^{-}$ ion is smallest, it is polarised.
$\therefore$ AgF will have highest ionic character and hence highest melting point.
$(\because$ Ionic compounds have greater melting point than covalent compound)