Fill in the blank with an appropriate Preposition:

The Soldiers are _____ War.

at

The correct answer is Option (1) → at

The correct phrase is "at war", which is commonly used to indicate a state of conflict or hostility. Here's why the other options do not work in this context:

• "on war": Not a standard phrase in English. "On" would be incorrect here.
• "in war": While this could be used in certain contexts, it generally refers to being involved in warfare rather than the general state of conflict.
• "with war": This phrase doesn't fit idiomatically or semantically here.

Thus, "The soldiers are at war" is the correct usage.