Calculate the pH of a .02M HBrO solution Ka for hypobromous acid is 2.0*10^-9 I got 10.5 but it says it isn't right

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

What are the first two quantum numbers for the electrons located in subshell 4d? what are the first three quantum numbers for the electrons located in subshell 2s? how many electrons can be held in a sublevel l = 3? how many electrons can be held in the energy level n = 4? how many electrons in an atom can share the quantum numbers n = 4 and l = 3?

What must be in balance for temperatures to remain constant?