Which one is correct?

"B" is the right answer, because e.g. is used to provide examples while i.e used to clarify the mentioned before it.

so it should be: Mr. Nicson suffers from AD (i.e., Alzheimer's disease).

E.g. means for example (from the Latin exempli gratia) I.e. means in other words or that is (from the Latin id est). 

e.g.

The abbreviation e.g. is used to provide an example: Examples: The buffet provided excellent variety, e.g., vegetarian and non-vegetarian soups, Italian and French breads, and numerous sweets. (e.g. = for example)

i.e.

The abbreviation i.e. is used to restate an idea more clearly or offer more information. Examples: It happened in August; i.e., two months ago. (i.e. = in other words)The Correct Answer is Numper B.

As far as I know, e.g. = for example ; i.e. = that is ; now you make your pick :)

The Answer is (B), I.E and E.G are Latin phrases: 

I.E. stands for "id est," which means, "in other words." E.G. stands for "exempli gratia," which means "for example."

. : the correct sentence is the second:  Mr. Nicson suffers from AD (i.e., Alzheimer's disease)

  because AD is the abriviation of the alzheimer disease and by using  i.e which is the abriviation of it means so in this case the second sentence is correct 

The answer is B as eg denotes 'for example' and ie denotes 'that is' and AD is an abbreviation for Alzheimers Disease therefore ie is an explanation of the term. Eg would only be appropriate if there were multiple conditions referred to as AD.

I think The Correct Answer is Numper (A). Mr. Nicson suffers from AD (e.g., Alzheimer's disease).