Explanation:
- The formula of the cobaltamine is CoCI3.xNH3, which means that there are x molecules of ammonia (NH3) associated with each molecule of CoCI3.
- When this compound is reacted with AgNO3 solution, one third of the chloride (CI) is precipitated, which means that one of the three chloride ions is replaced by Ag+ ion.
- This reaction can be represented as:

CoCI3.xNH3 + AgNO3 → CoCI2.xNH3 + AgCI + NO3-

- To determine the structure of the cobaltamine, we need to consider the coordination number of cobalt (Co), which is six.
- Based on this coordination number, the possible structures for the cobaltamine are:

a) [Co(NH3)6]CI3 - This structure has all six ammonia molecules associated with cobalt and three chloride ions as counter ions. However, when one of the chloride ions is replaced by Ag+ ion, the resulting compound would be [Co(NH3)6]CI2, which is not consistent with the observation in the question.

b) [Co(NH3)5]CI2 - This structure has five ammonia molecules associated with cobalt and two chloride ions as counter ions. When one of the chloride ions is replaced by Ag+ ion, the resulting compound would be [Co(NH3)5]CI, which is not consistent with the observation in the question.

c) [Co(NH3)4CI2]CI - This structure has four ammonia molecules and two chloride ions associated with cobalt, and one chloride ion as counter ion. When one of the chloride ions is replaced by Ag+ ion, the resulting compound would be [Co(NH3)4CI2]AgCI, which is consistent with the observation in the question.

d) [Co(NH3)5H2O]CI3 - This structure has five ammonia molecules and one water molecule associated with cobalt, and three chloride ions as counter ions. When one of the chloride ions is replaced by Ag+ ion, the resulting compound would be [Co(NH3)5H2O]CI2AgCI, which is not consistent with the observation in the question.

Therefore, the correct structure for the cobaltamine is [Co(NH3)4CI2]CI.