In cation exchange chromatography, the stationary matrix is negatively charged and binds positively charged molecules; species with negative or least positive net charge elute first, while strongly positive species bind tightly and elute last.
At pH 6.0:

• Glutamic acid ($pK_R = 4.25$): Since $pH \gt pK_R$, the side-chain carboxyl group is deprotonated ($-COO^-$). Net charge $\approx -1$. It is repelled by the negative resin and elutes FIRST.
• Histidine ($pK_R = 6.0$): Since $pH = pK_R$, the imidazole side chain is 50% protonated. Net charge $\approx +0.5$. It binds weakly and elutes SECOND.
• Lysine ($pK_R = 10.5$): Since $pH \lt pK_R$, the epsilon-amino group is fully protonated ($-NH_3^+$). Net charge $\approx +1$. It binds strongly to the resin and elutes LAST.

According to Beer-Lambert's law, nucleic acids absorb ultraviolet light maximally at $260 \text{ nm}$ due to the conjugated ring systems of purine and pyrimidine bases. By standard convention:
$1.0 \; A_{260} \text{ unit} = 50 \; \mu\text{g/mL}$ for double-stranded DNA (dsDNA)
$1.0 \; A_{260} \text{ unit} = 40 \; \mu\text{g/mL}$ for single-stranded RNA (ssRNA)
$1.0 \; A_{260} \text{ unit} = 33 \; \mu\text{g/mL}$ for single-stranded oligonucleotides/ssDNA.

• The standard quantitative spectrophotometric determination of proteins at 280 nm ($A_{280}$) depends overwhelmingly on aromatic side chains and disulfide bonds:
• Tryptophan: Dominant contributor, with $\lambda_{\text{max}} \approx 280\text{ nm}$ and molar extinction coefficient $\varepsilon_{280} \approx 5,690\text{ M}^{-1}\text{cm}^{-1}$.
• Tyrosine: Substantial contributor, with $\lambda_{\text{max}} \approx 274\text{ nm}$ and $\varepsilon_{280} \approx 1,280\text{ M}^{-1}\text{cm}^{-1}$.
• Cystine (disulfide bonds): Measurable contribution, with $\varepsilon_{280} \approx 120\text{ M}^{-1}\text{cm}^{-1}$.
• Phenylalanine has an isolated benzene ring with narrow vibronic fine structure bands centered sharply around $\lambda_{\text{max}} = 257\text{ nm}$ ($\varepsilon_{257} \approx 200\text{ M}^{-1}\text{cm}^{-1}$), and its extinction coefficient drops to near zero at 280 nm ($\varepsilon_{280} \lt 10\text{ M}^{-1}\text{cm}^{-1}$).
• Thus, Phenylalanine does NOT contribute significantly to UV absorbance at 280 nm (Option 3).

• Chromatographic column efficiency and resolution ($R_s$) are directly governed by the number of theoretical plates ($N$), given by the relationship:
  $$N = \frac{L}{\text{HETP}}$$
  where $L$ is column length and $\text{HETP}$ ($H$) is the height equivalent to a theoretical plate.
• (A) is true: Chromatographic resolution is proportional to $\sqrt{N}$; increasing theoretical plates sharpens elution peaks and improves separation.
• (B) is true: Because $N = L / H$, decreasing HETP increases the number of theoretical plates per unit length, directly improving efficiency.
• (C) is false: Decreasing column height ($L$) reduces $N$ ($N = L/H$), leading to peak broadening and poorer separation.
• (D) is true: According to the van Deemter equation ($H = A + \frac{B}{u} + C\cdot u$), the eddy diffusion term ($A = 2\lambda d_p$) and stationary phase mass transfer term ($C_s \propto d_p^2$) decrease drastically with smaller particle diameter ($d_p$), reducing HETP and maximizing separation efficiency (the basis of HPLC and UPLC).
  
  (F) Hence, (A), (B) and (D) only result in enhanced separation (Option 1).