Let us suppose that we have 1 mol of FeCr2O4. I'm going to use approximate masses because I have no idea what your periodic table will say. Just put in the exact masses from your periodic table.
Fe = 56
Cr*2 = 2*52 = 104
O4 = 4*16 = 64
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Total = 56 + 104 + 64 = 224
The % oxygen = (64 / 224) * 100 = 28.5 % but none of your answers match this. Perhaps you are talking about Fe2(Cr2O4)3 The brackets make all the difference in the world.
Without going through all the detail I did before, The molecular mass is
Fe * 2 = 112
Cr * 6 = 312
O * 12 = 192
The total molecular mass = 616
The % Oxygen = (192 / 616) * 100 = 31% roughly. That answer isn't there either.
Let's wait and see who else answers.
Answer: e) all of these
Explanation:
Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Copper
Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: water 
, carbon dioxide 
Mixtures are not pure substances as they consist of elements and compounds combined physically and not in any fixed ratio. Example: Air
Thus all given substances are pure substances.
Answer:
16
Explanation:
Because the sum of all electron in that compound should be 41 and as it has one electron extra ,total no. of electrons are 42 .
So if we add 26 +16 we get 42
Hence it's correct answer
Hey there!
A half-life means after a certain amount of time, half of that substance will be gone/changed after that time.
How many half-lives are in 16 days?
Multiply 16 by 24 (to get the total hours) and divide that by 2.5.
That is 153.6 half-lives.
35(0.5)^(153.6) represents the equation for this.
Simplify this and get 8.88 x 10^(-45).
There will be 2.02 x 10^(-45)g of germanium-66 sample remaining after 16 days.
Hope this helps!
