2 H2 (g) —> 2 H2O (g)

Calculate the mass of oxygen gas, O2, required to produce 12.90 moles of water, H20

Molar mass H2= 2.016 g/mol
Molar mass O2= 32.00 g/mol
Molar mass = 18.02 g/mol

mole=mass/molar mass

mass=mole×molar mass

mass=12.90mole×18g/mole

mass=232.2g

може ли да зареждате повече информация, моля

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.