How hot would it need to be to boil the oceans?

The salt would raise the boiling point by at least 5C, so I would say you would need a minimum of 110C (230F) evenly over the ocean floor. Applying this constantly should eventually achieve a boil, even in the deepest trenches. Although this might take years, possibly decades.

On the other hand 70% of volcanic eruptions take place in the oceans and lava is 700-1200C (1,292 to 2,192 °F).

I would say you would need at least 100 times that just to bring it to a reasonable boil in a reasonable amount of time (amount of time it takes to boil water on a stove). So about 70,000-120,000C (129,200 - 219,200F). This would have to be applied evenly throughout.

If you want it in less than one second, you would probably have to go a lot hotter.

Well the boiling point of water is 100*c however you are asking of sea water, which contains salt. Salt raises the boiling point. The salt content varies from place to place. So tbh around 115*c. If you ask about instatly boiling the water, you will need enough infra red (heat) for alot of water. That would be a VERY LARGE number indeed.

456 C

Hot

50 degrees?

probably 3 times more.. OVER 9000!!

212. might take a while though