What is the domain with four kingdoms or organisms that have cells with nuclei?

Used the balanced equation 2h2+ o2 - -> 2h2o. if you have 7.2 grams of o2 , how many grams of h2o can you produce ?

The excretory system,need answers for all: )

Suppose you mix one mole of sulfuric acid (h2so4) with 1 mole of sodium hydroxide(naoh). why does the ph of the solution remain below 7? ( explain so i can get better understanding! )