The arithmetic eleven natural numbers mean of first is :

5
5.5
8
6

The correct answer is (b) 5.5.

The arithmetic mean of a set of numbers is the sum of the numbers divided by the number of numbers. In this case, the set of numbers is the first eleven natural numbers, which are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11. The sum of these numbers is 55. The number of numbers in the set is 11. Therefore, the arithmetic mean is 55 / 11 = 5.5.

Option (a) is incorrect because 5 is not the arithmetic mean of the first eleven natural numbers. Option (c) is incorrect because 8 is not the arithmetic mean of the first eleven natural numbers. Option (d) is incorrect because 6 is not the arithmetic mean of the first eleven natural numbers.