Given that the question asks specifically for conventional weapons (so ruling out Hiroshima and Nagasaki), and is now limited to a 24 hour period in history, you are probably looking at Operation Meetinghouse (https://en.wikipedia.org/wiki/Bombing_of_Tokyo_(10_March_1945)#Casualties) where 279 B-29 bombers dropped 1,665 tons of bombs on Tokyo on the night of 9–10 March, 1945.
Approximately 100,000 people were killed.
The bombs dropped by the B-29s were mostly E-46 cluster bombs and M-47 incendiary bombs (https://en.wikipedia.org/wiki/M47_bomb). The E-46 cluster bombs each contained 38 M-69 incendiary bomblets (https://en.wikipedia.org/wiki/M69_incendiary). The M-69 bomblet itself contained napalm.
If you are interested in more details about the weapons employed, you might find Fire warfare : Incendiaries and flame throwers (https://archive.org/details/firewarfareincen00unit/page/6), published in 1946 by the United States. Office of Scientific Research and Development of interest (especially Chapter 1: Incendiary Bombs and Clusters).
The firestorm resulting from the raid caused more than 80,000 casualties. The exact number of dead will never be known, but:
- 79,466 bodies were recovered and recorded.
- The Tokyo Director of Health estimated 83,600 people were killed and 40,918 were wounded.
- The Tokyo Fire Department estimated that 97,000 were killed and 125,000 wounded.
- The Tokyo Metropolitan Police Department estimated that a total of 124,711 people were killed or wounded in the raid.
- A report by the United States Strategic Bombing Survey (https://archive.org/details/U.s.StrategicBombingSurveyReport90IncendiaryAttacksOnJapan/page/n71) estimated the casualties to have been 87,793 killed and 40,918 injured.
(Figures from Frank, 1999, except as otherwise cited)
The British Pathé news archive has newsreel footage (https://www.britishpathe.com/workspaces/df699ffd537d4e0c74710ad015dfd64d/V8Nk94zZ) which shows the devastation caused by the raid.
Most historians estimate the total number killed on that night to be between 90,000 and 100,000, but some argue that the actual number may have been much higher.
- Richard B. Frank: The End of the Imperial Japanese Empire (https://books.google.co.uk/books/about/Downfall.html?id=cJXtAAAAMAAJ), 1999