Explanation:

Total float, free float, interfering float, and independent float are important concepts in project management. Let's understand each of them and then identify the incorrect statement.

Total Float:

Total float is the amount of time that an activity can be delayed without delaying the project completion date. It is the difference between the late start and early start times of an activity. Total float can be calculated using the following formula:

Total Float = Late Start Time - Early Start Time

Free Float:

Free float is the amount of time that an activity can be delayed without delaying the early start of its successor activity. It is the difference between the early finish time of the successor activity and the early start time of the current activity minus its duration. Free float can be calculated using the following formula:

Free Float = Early Start Time of Successor - (Early Start Time of Activity + Duration)

Interfering Float:

Interfering float is the amount of time that an activity can be delayed without delaying the late start time of a succeeding activity. It is the difference between the late finish time of the succeeding activity and the late start time of the current activity minus its duration. Interfering float can be calculated using the following formula:

Interfering Float = Late Finish Time of Successor - (Late Start Time of Activity + Duration)

Independent Float:

Independent float is the amount of time that an activity can be delayed without delaying the early start time of any succeeding activity or the project completion date. It is the difference between the late start time of the current activity and the early finish time of its predecessor minus its duration. Independent float can be calculated using the following formula:

Independent Float = Early Finish Time of Predecessor - (Late Start Time of Activity + Duration)

Now, let's identify the incorrect statement from the given options:

a)Total float is the aggregate of free, interfering and independent float. - This statement is incorrect. Total float is the aggregate of free float and interfering float, but not independent float.

b)For each critical activity – total, free and independent floats are equal to zero. - This statement is correct. Critical activities have no float, whether it is total, free, or independent.

c)An activity with some free float cannot be a critical activity. - This statement is incorrect. An activity with some free float can be a critical activity if its free float is less than or equal to zero.

d)Interfering float is the excess of total float over the free float. - This statement is incorrect. Interfering float is the difference between total float and free float.

Therefore, option 'A' is the incorrect statement.