Pattern 1: Bohr Energy Calculations (2-3 questions/year)

What they ask:

• Energy of electron in nth orbit of H or $He^{+}$, $Li^{2+}$
• Energy of transition ($\Delta E$)
• Wavelength/frequency of emitted photon
• KE and PE of electron

Key formula: $E_n = -\frac{13.6 Z^2}{n^2} \text{ eV}$

Most common trap: Forgetting $Z^{2}$ factor; getting sign wrong.

Pattern 2: Quantum Number Sets (1-2 questions/year)

What they ask:

• Identify invalid quantum number sets
• What orbital do given quantum numbers describe
• How many electrons with given n or l

Key rule: l must be from 0 to (n-1). If l ≥ n → invalid. mₗ must be between -l and +l.

Pattern 3: Spectral Lines Counting (1 question/year)

What they ask:

• How many lines from level n
• How many lines in a specific series from level n
• Maximum wavelength / minimum wavelength in a series

Key formula: $\text{Lines} = \frac{n(n-1)}{2}$

Pattern 4: Electronic Configuration (1-2 questions/year)

What they ask:

• Configuration of Cr, Cu (anomalous)
• Number of unpaired electrons in Fe, $Fe^{3+}$, Mn, etc.
• Configuration of transition metal ions

Key rule: 4s empties before 3d when forming cations.

Pattern 5: Assertion-Reason (recent trend — 1-2/year)

Topics tested in A-R format:

• Photoelectric effect (intensity vs frequency)
• Bohr vs Heisenberg
• Angular momentum quantization
• Extra stability of half-filled/full-filled subshells

NEET Year-wise Frequency