For A: Molar mass of H2O=18 g/mol. Moles of H2O=181.8×10−3=10−4. Since each H2O molecule has 3 atoms, the number of atoms = 3×10−4×NA.
For B: Molar mass of H2SO4=98 g/mol. Moles of H2SO4=989.8×10−3=10−4. Since each H2SO4 molecule has 7 atoms, the number of atoms = 7×10−4×NA.
For C: Molar mass of C=12 g/mol. Moles of C=121.8×10−3=1.5×10−4. The number of atoms = 1.5×10−4×NA.
For D: Molar mass of NaCl=58.5 g/mol. Moles of NaCl=58.55.85×10−3=10−4. Since each NaCl formula unit has 2 atoms, the number of atoms = 2×10−4×NA.
Thus, the correct matching is A-III, B-IV, C-II, D-I.
Answer: A-III, B-IV, C-II, D-I