Which battle or event caused the most Japanese casualties?

a. the Battle of Iwo Jima

b. the bombing of Hiroshima

c. the bombing of Nagasaki

d. the Battle of Okinawa

I choose letter b. the bombing of Hiroshima. It resulted in a total of almost 150,000. Apart from those killed in the initial blast, there were those who later succumbed to burns and radiation sickness. Three days later the Americans dropped another bomb in Nagasaki which led to the surrender of the Japanese and the end of the war.