War always has a baneful effect on the people of a nation.

Answer: Option C

Unpleasant : causing discomfort, unhappiness, or revulsion; disagreeable.
Foul : offensive to the senses, especially through having a disgusting smell or taste or being dirty.
Pernicious : having a harmful effect, especially in a gradual or subtle way.
Beneficial : resulting in good; favourable or advantageous.
Baneful : harmful or destructive.

Synonym of Baneful is Pernicious