Q.

The colour of iodine is different in different conditions which of the following statements is/are correct for iodine

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a

Solid iodine is blackish violet but gaseous iodine is violet in colour.

b

 I2  dissolved in  CS2,CHCl3  or  CCl4  is violet.

c

 I2  dissolved in n- hexane, benzene, ethanol and pyridine are violet, purple, brown and yellow respectively, but on adding pyridine to solutions of  I2  in n-hexane, benzene and ethanol also changes to yellow

d

In gaseous state form  F2 to I2 the intensity of colour of  halogens increases

answer is A, B, C, D.

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Detailed Solution

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In gaseous  I2 colour arises due to electronic transition from  π*MOtoσ*MO, for which energy is absorbed in yellow region. So it appear violet in colour when  I2 is dissolved in solvents such as  CS2,CHCl3,CCl4 which do not contain LP, the electronic transition is from up  πp*MO  to  σp*MO  so violet. But when dissolved in solvents such as pyridine, alcohol etc. While contain LP, that can donate LP to  σ*pz.  So electronic transition between  πp*MOtoσ*2pMO is not possible. Due to charge transfer from solvent to  I2 molecule brown colour arises. With increase in size of halogen atom in the group the energy difference between  π2p*andσ*2p orbitals goes on decreasing. This causes increase in the intensity of colour.

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