Chemistry - Mole Concept Question with Solution | TestHub

Here's a brief solution to the problem:

Option A: 0.5 g-molecule of oxygen contains $\frac{N_A}{4}$ oxygen molecules.

1 g-molecule of $O_2$ contains $N_A$ molecules. Therefore, 0.5 g-molecule contains $0.5\times N_A=\frac{N_A}{2}$ molecules. This statement is incorrect.

Option B: Total electrons present in 0.5 g-atom of oxygen is $4N_A$.

1 g-atom of oxygen contains $N_A$ atoms. Each oxygen atom has 8 electrons. Therefore, 0.5 g-atom of oxygen contains $0.5\times N_A$ atoms, and the total number of electrons is $0.5\times N_A\times 8=4N_A$. This statement is correct.

Option C: Mass of $3.01\times 10^{23}$ molecules of ammonia is 8.5 g.

The molar mass of ammonia ($N{H}_3$) is 14 + 3(1) = 17 g/mol.

$N_A=6.022\times 10^{23}$ molecules weigh 17 g.

$3.01\times 10^{23}$ molecules weigh $\frac{17}{6.022\times 10^{23}}\times 3.01\times 10^{23}\approx \frac{17}{2}=8.5$ g. This statement is correct.

Option D: Number of atoms present in 11.2 litres of chlorine at 1 atm & 273 K is $6.022\times 10^{23}$.

1 mole of any gas at standard temperature and pressure (STP) occupies 22.4 L.

11.2 L of chlorine ($C{l}_2$) at STP corresponds to $\frac{11.2}{22.4}=0.5$ moles of $C{l}_2$.

Since each $C{l}_2$ molecule has 2 atoms, 0.5 moles of $C{l}_2$ contain $0.5\times 2\times N_A=N_A=6.022\times 10^{23}$ atoms. This statement is correct.

The correct options are B, C and D.