JEE Main 2026 — Some Basic Concepts of Chemistry Question with Solution

For A: Molar mass of $H_{2}O=18$ g/mol. Moles of $H_{2}O=\frac{1.8\times 10^{-3}}{18}=10^{-4}$. Since each $H_{2}O$ molecule has $3$ atoms, the number of atoms = $3\times 10^{-4}\times N_A$.

For B: Molar mass of $H_{2}S{O}_4=98$ g/mol. Moles of $H_{2}S{O}_4=\frac{9.8\times 10^{-3}}{98}=10^{-4}$. Since each $H_{2}S{O}_4$ molecule has $7$ atoms, the number of atoms = $7\times 10^{-4}\times N_A$.

For C: Molar mass of $C=12$ g/mol. Moles of $C=\frac{1.8\times 10^{-3}}{12}=1.5\times 10^{-4}$. The number of atoms = $1.5\times 10^{-4}\times N_A$.

For D: Molar mass of $NaCl=58.5$ g/mol. Moles of $NaCl=\frac{5.85\times 10^{-3}}{58.5}=10^{-4}$. Since each $NaCl$ formula unit has $2$ atoms, the number of atoms = $2\times 10^{-4}\times N_A$.

Thus, the correct matching is A-III, B-IV, C-II, D-I.

Answer: A-III, B-IV, C-II, D-I