Answer
(a) $S_2Cl_2$
(b) $ICl$
(c) $NI_3$
Work Step by Step
(a) "Di-" represents 2, so we have two sulfurs and two chlorides: $S_2Cl_2$.
(b) "Mono-" represents 1, so we have only one chloride, and since the number of iodines is not represented, we assume it is equal to 1: $ICl$ (This is because Iodide and Chloride have equal charges, so they should be equal in number in a neutral compound.)
(c) "Tri-" represents 3, so this compound has 3 iodides, and since the number of nitrogens is not represented, we assume it is equal to 1: $NI_3$
