Mass or volume-------------
This problem may easily solved by applying the conservation of mass, which states that the total mass before and after a change is constant because mass can neither be created nor destroyed.
We know that water consists of only hydrogen and water, and that there are no other reactants except hydrogen and oxygen. Thus:
Mass of reactants = Mass of product
mass of hydrogen + mass of oxygen = mass of water
4 + mass of oxygen = 36
mass of oxygen = 32 grams
Answer: Option (d) is the correct answer.
Explanation:
A tetarhedral geometry is the geometry which includes four atoms bonded to the central atom and it does not contain any lone pair of electron.
For example, 
has tetrahedral geometry.
Thus, we can conclude that a molecule which contains four bonded pairs of electrons and zero lone pairs. The name of the molecular geometry is tetrahedral.
They did not repeat their tests multiple times.
Reason being is using the same stopwatch doesn’t matter and changing the reactants won’t help, and you without a doubt need more than one person collecting the data so,
They did not repeat their tests multiple times is the answer.
____NaNO3 + ___PbO --> ___Pb(NO3)2 + ___Na[2]O
To balace the eqaution, you need to have the same number of atoms for each element on both the reactant (left) and product (right) side.
To start off, you wanna know the number of atoms in each element on both sides, so take it apart:
[reactants] [product]
Na- 1 Na- 2
N- 1 N- 2(it's 2 because the the subscript [2] is outside of the parenthesis)
O- 4 O- 7 (same reason as above)
Pb- 1 Pb- 1
Na is not balanced out, so add a coefficient to make it the same on both sides.In this case, multiply by 2:
2NaNO3
Now Na is balanced, but the N and O are also effected by this, so they also have to be multiplied by 2 and they become:
Na- 2 Na- 2
N- 2 N- 2 (it balanced out)
O- 7 (coefficient times subscript, plus lone O) O- 7 (balanced out)
Pb was already balanced so no need to mess with it, just put a 1 where needed (it doesn't change anything).
Now to put it back together, it will look like this:
2NaNO3 + 1PbO --> 1Pb(NO3)2 + 1Na[2]O
