Verified Answer :

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The solution is as follows:
Convert 3.00 g Na2Cr2O7 into mol. To do this, we must know the molar mass. Molar mass of Na2Cr2O7 is 261.97 g/mol
Mol Na2Cr2O7 = (3.00 g Na2Cr2O7)( mol / 261.97 g) = 0.01145 mol
In 1 mol of Na2Cr2O7 there are 7 mol of O (oxygen). Therefore:
Mol O = 0.01145 mol Na2Cr2O7 (7 mol O/ 1 mol Na2Cr2O7) = 0.08016 mol O
In 1 mol of any substance, there are 6.02 x 10^23 atoms
Atoms of O = 0.08016 mol O ( 6.02 x 10^23 atoms / mol O) = 4.8257 x 10^22 atoms

Answer : The number of oxygen atoms are, \(4.8\times 10^{22}\)

Explanation : Given,

Mass of \(Na_2Cr_2O_7\) = 3 g

Molar mass of \(Na_2Cr_2O_7\) = 261.97 g/mole

First we have to calculate the moles of \(N_2O_3\)

\(\text{Moles of }Na_2Cr_2O_7=\frac{\text{Mass of }Na_2Cr_2O_7}{\text{Molar mass of }Na_2Cr_2O_7}=\frac{3g}{261.97g/mole}=0.0114mole\)

As we know that \(Na_2Cr_2O_7\) contains 2 number of sodium atoms, 2 number of chromium atoms and 7 number of oxygen atoms.

Now we have to calculate the number of atoms of oxygen.

As, 1 mole of \(Na_2Cr_2O_7\) contains \(7\times 6.022\times 10^{23}\) number of oxygen atoms

As, 0.0114 mole of \(Na_2Cr_2O_7\) contains \(0.0114\times 7\times 6.022\times 10^{23}=4.8\times 10^{22}\) number of oxygen atoms

Therefore, the number of oxygen atoms are, \(4.8\times 10^{22}\)

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