Q.(a)

(i) Molar volume is the volume of one mole of a gas at STP (22.4 L at 0°C, 1 atm). (ii) Bohr's atomic model has several key limitations: it fails for multi-electron atoms, cannot explain fine spectral line splitting, cannot account for chemical bonding, and violates both the Heisenberg uncertainty principle and the wave nature of matter.

(i) Molar Volume:

Molar volume is defined as the volume occupied by one mole of a substance. For gases, at Standard Temperature and Pressure (STP: 0°C/273.15 K and 1 atm pressure), one mole of any ideal gas occupies 22.4 litres — this is a direct consequence of Avogadro's law (equal volumes of gases at the same T, P contain equal moles). Under the newer IUPAC definition of STP (0°C, 1 bar), this molar volume is 22.7 L.

(ii) Limitations of Bohr's atomic model:

1. It could successfully explain the spectrum of hydrogen (and other single-electron/hydrogen-like species) but failed to correctly predict the spectra of multi-electron atoms.
2. It could not explain the finer details (splitting) of spectral lines observed under a magnetic field (Zeeman effect) or an electric field (Stark effect).
3. It could not explain how atoms combine to form covalent bonds/molecules, i.e. it gave no picture of chemical bonding. …