Iodoform gives a precipitate with AgNO3 on heating but chloroform does not because -

Explanation

Carbon-iodine bond is quite weak (`213.4 kJ mol^(-1)`) as compared to carbon-chlorine bond (`326.4 kJ mol^(-1)`). Therefore, when iodoform is heated with `AgNO_(3)` solution, C-I bond gets cleaved easily and iodide ions react with `AgNO_(3)` solution to give precipitate of Agl. On the other hand, C-Cl bond does not get cleaved.