Step 1: What is a bathochromic shift?
In UV-visible spectroscopy, the position of an absorption band can shift when the structure of a molecule changes (for example, by adding a substituent) or when the solvent changes. These shifts have specific names.
Step 2: Recall the four key spectral shift terms.
Bathochromic shift (red shift): movement to a higher wavelength (longer wavelength). Hypsochromic shift (blue shift): movement to a lower wavelength (shorter wavelength). Hyperchromic effect: increase in absorbance (molar absorptivity). Hypochromic effect: decrease in absorbance.
Step 3: Evaluate the wrong options.
Option 1 (shift to lower wavelength) describes a hypsochromic or blue shift, not bathochromic. Option 3 (decrease in absorbance) describes a hypochromic effect. Option 4 (increase in intensity) describes a hyperchromic effect.
Step 4: Confirm Option 2.
A bathochromic shift is a shift to a higher (longer) wavelength. Since red light has a longer wavelength than blue light, it is also called a red shift. It is caused by the addition of conjugation, auxochromes, or a change to a more polar solvent.
Step 5: Memory hook.
Bath = longer (think of how time seems longer in a bath). Bathochromic = shift to higher wavelength.
Answer: Option (2) — Shift to higher wavelength