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Question

what happens when you add a small amount of manganese (IV) oxide powder to 50 ml of hydrogen peroxide solution in a 250-mL beaker. cover the beaker with a waatch glass for 15 seconds. and then a wood splint is inserted at the top of the beaker. and then the hydrogen peroxide and the manganese starts fizzing. and the hydrogen peroxide turns grey. and if you put the wood splint near it, it catches on fire

Answer 1

MnO2 is a catalyst that causes H2O2 to decompose quickly into water & oxygen

the beaker filled with an oxygen rich environment, which supports the combustion of the splint.  in O2 of that concentration, the ignition temp of wood is lowered. so a hot glowing splint is hot enough to auto-ignite

the turning grey is juct the color of wet MnO2

the fizz is oxygen gas being produced