Option 1 -> "propagated programmes" is awkward; propagate means to spread ideas, not to start programmes.
Option 2 -> "embarked" requires "on" (embarked on programmes), making "embarked programmes" grammatically incorrect.
Option 3 -> "initiated programmes" is grammatically correct and logically sound; nations that have started development programmes naturally encounter barriers during implementation.
Option 4 -> "suspended programmes" contradicts the sentence logic; suspended programmes wouldn't be running into barriers since they're halted.
Hence, Option 3: initiated -> fits perfectly as it means "begun" or "started," and nations that have started economic development programmes would naturally face unexpected obstacles during their execution -> correct