1.  calculate the mass of 1 molecule of BENZENE(C6H6)
2. calculate the number of grams of oxygen in 0.10 mole of Na2CO3.10H2O

molar mass of benzene= 78.114 g/mol

The mass of one mole ( = 6.02 x 10²³ molecules) is 78.114 g

the mass of one molecule is 78.114 / 6.02 x 10²³ = 1.30 x 10^-22 g

The mass of one molecule of benzene is 1.30 x 10 ^-22 g

2.

Since 1 mole of Na ₂ CO ₃ .10H ₂ 0 = 6.022 X10 ²³ molecules of Na ₂ CO ₃ .10H ₂ 0

So 0.1 mol of Na ₂ CO ₃ .10H ₂ O will have = 6.022 X10 ²³ X0.1 molecules of Na ₂ CO ₃ .10H ₂ 0

Now we know that each molecule contains 13 O-atoms,

Total no. of O- atoms = 6.022 X10 ²² X 13

hence O ₂ molecules will be = 6.022 X10 ²² X 13 /2= 6.022 X10 ²² X 6.2

Now further, 6.022 X10 ²³ molecules of Oxygen = 1 mol Oxygen gas .

Thus, 6.022 X10 ²² X 6.2 molecules of Oxygen will contain= 6.022 X10 ²² X 6.2 / 6.022 X10 ²³ moles of oxygen

= 0.62 mol of oxygen

Now as one mol oxygen = 32 gm of oxygen

So, 0.62 mol oxygen = 32 X 0.62= 19.84 gm of Oxygen gas.

hope it helps u