Question

Select correct statements:

• A. Colours of the halogens ($F_2,C{l}_2,B{r}_2,I_2$) in the gas phase are complimentary colours.
• B. Colour is due to transition of an electron from the highest occupied ${\pi }^{\ast }$ molecular orbital to the lowest occupied ${\sigma }^{\ast }$ molecular orbital.
• C. $Cl{O}_2$ is paramagnetic due to unpaired electrons.
• D. $Cl{O}_2$ dimerises to $C{l}_2{O}_{4}asN{O}_2$ dimerises to $N_2{O}_4$.

Answer 1

Answer: (A), (B), (C)

The correct options are
A Colours of the halogens ($F_2,C{l}_2,B{r}_2,I_2$) in the gas phase are complimentary colours.
B Colour is due to transition of an electron from the highest occupied ${\pi }^{\ast }$ molecular orbital to the lowest occupied ${\sigma }^{\ast }$ molecular orbital.
C $Cl{O}_2$ is paramagnetic due to unpaired electrons.

A. The colours of the halogens in the gas phase are complimentary. They absorb light of one wavelength the colour that appears is complimentary. Thus, the option A is correct.

B. An electron transition from the highest occupied $\pi \ast$ molecular orbital to the lowest unoccupied $\sigma \ast$ molecular orbital gives rise to the colour. Thus, the option B is correct.

C. $Cl{O}_2$ contains unpaired electrons. hence, it is paramagnetic in nature. Thus, the option C is correct.

D. $Cl{O}_2$ exists as a monomer but $N{O}_2$ dimerizes to $N_2{O}_4$. Hence, the option D is incorrect.