Electrolysis uses electrical current to break water molecules into oxygen gas and hydrogen gas. how do you know that this is a chemical change?

Find the mass, in grams, of 5.00*10^23 molecules of f2

How many grams of ammonia would be produced by the decomposition of 16.93 mlof hydrazine? (the density of hydrazine is 1.021g/ml)

How many lone pairs of electrons are on the central atom of no3- and what is the molecular shape? one, trigonal planar zero, trigonal pyramidal zero, trigonal planar one, tetrahedral one, trigonal pyramidal