When an electron jumps directly from an orbit of n = 4 to n = 2,

Analyze the question: An electron moves from a higher energy level (n = 4) to a lower one (n = 2) in a single, direct jump. We need to say what happens to the energy.

Concept: In the Bohr model, the energy of an electron in the nth orbit is

Eₙ = −13.6 / n² eV (for hydrogen)

• Moving to a higher level (e.g., n = 2 → n = 4) requires energy, so a photon is absorbed.
• Moving to a lower level (e.g., n = 4 → n = 2) releases energy, so a photon is emitted.

Solution:

• E₄ = −13.6 / 16 = −0.85 eV
• E₂ = −13.6 / 4 = −3.40 eV

Energy change: ΔE = E₂ − E₄ = −3.40 − (−0.85) = −2.55 eV

The negative sign shows the electron loses 2.55 eV. This energy leaves as one photon, with energy hf = 2.55 eV. This is a line in the Balmer series (visible light, blue-green, about 486 nm).

Because the jump is direct (4 → 2 in one step), only one photon is emitted. Two photons would be emitted only if the electron went in two steps (4 → 3, then 3 → 2).

Answer: Option B, a photon is emitted.

Tip: Remember "Down = Disappears energy (emit), Up = Used energy (absorb)". Also, count the number of jumps: one direct jump means one photon.