Among the following, choose the ones with equal number of atoms.

A. 212 g of Na₂CO₃ (s)   [molar mass = 106 g]
B. 248 g of Na₂O (s)   [molar mass = 62 g]
C. 240 g of NaOH (s)   [molar mass = 40 g]
D. 12 g of H₂ (g)   [molar mass = 2 g]
E. 220 g of CO₂ (g)   [molar mass = 44 g]

Choose the correct answer from the options given below:

The correct option is A, B, and D only.

To find the ones with an equal number of atoms, we need to calculate the total number of atoms in each given sample. The total number of atoms in a substance can be calculated using the formula:
Number of atoms = (Mass of substance / Molar mass) × Number of atoms per formula unit/molecule × N_A
where N_A is Avogadro's number ($N_A$).

Let's calculate the total number of atoms for each case step-by-step:

A. 212 g of Na₂CO₃ (s) [molar mass = 106 g/mol]
Number of moles of Na₂CO₃ = $\frac{212}{106}=2\text{ mol}$
Each formula unit of Na₂CO₃ contains 2 Na + 1 C + 3 O = 6 atoms.
Total number of atoms = $2\times 6\times N_A=12N_A$

B. 248 g of Na₂O (s) [molar mass = 62 g/mol]
Number of moles of Na₂O = $\frac{248}{62}=4\text{ mol}$
Each formula unit of Na₂O contains 2 Na + 1 O = 3 atoms.
Total number of atoms = $4\times 3\times N_A=12N_A$

C. 240 g of NaOH (s) [molar mass = 40 g/mol]
Number of moles of NaOH = $\frac{240}{40}=6\text{ mol}$
Each formula unit of NaOH contains 1 Na + 1 O + 1 H = 3 atoms.
Total number of atoms = $6\times 3\times N_A=18N_A$

D. 12 g of H₂ (g) [molar mass = 2 g/mol]
Number of moles of H₂ = $\frac{12}{2}=6\text{ mol}$
Each molecule of H₂ contains 2 H atoms.
Total number of atoms = $6\times 2\times N_A=12N_A$

E. 220 g of CO₂ (g) [molar mass = 44 g/mol]
Number of moles of CO₂ = $\frac{220}{44}=5\text{ mol}$
Each molecule of CO₂ contains 1 C + 2 O = 3 atoms.
Total number of atoms = $5\times 3\times N_A=15N_A$

Comparing the total number of atoms calculated:
- A has 12 N_A atoms.
- B has 12 N_A atoms.
- C has 18 N_A atoms.
- D has 12 N_A atoms.
- E has 15 N_A atoms.

Therefore, samples A, B, and D contain an equal number of atoms.