JEE Main · 2026 · 21 Jan 2026 · Shift 2 · Atomic Structure

The energy radiated in a transition is $\Delta E=13.6\left(\frac{1}{n_1^2}-\frac{1}{n_2^2}\right)$ eV. The first Paschen line ($4\to 3$) gives $13.6(1/9-1/16)=0.66$ eV; the second Balmer line ($4\to 2$) gives $13.6(1/4-1/16)=2.55$ eV; the third Paschen line ($6\to 3$) gives $13.6(1/9-1/36)=1.13$ eV; and the fourth Brackett line ($8\to 4$) gives $13.6(1/16-1/64)=0.64$ eV. Ranked from least to most energetic, the fourth Brackett line comes first, then the first Paschen line, then the third Paschen line, and the second Balmer line is highest, so the ascending order of energy is $\mathrm{D}<\mathrm{A}<\mathrm{C}<\mathrm{B}$.