Umesh is right. The correct answer is വാരണം.
Interestingly വാരണം comes from വാരണ which means obstruction. Elephants were used in war as obstructions.
വാണം is the തത്ഭവം of ബാണം, arrow.
രണം is from Sanskrit. It means "that which makes noise", of course, a war does make some noise.
Not sure about വാര. My dictionary says it is of Portuguese origin. Anybody has the details?