ARITHMETIC PROGRESSION............

The given sequence is not an AP.

1,-2,3,-4,-5...........................................n.(-1)ⁿ⁺¹

We have to find out the average of first 300 term.

Consider the sequence 1,-2,3,-4......................-300

every even number is negative and all odd numbers are positive. Also, the sum of two consecutive term is -1.

 For three hundred terms,

Sum = -1 + -1 +...............150 times

Sum = -150

Average = Sum/ No. of terms

Average of first 300 terms = -150/ 300 = -0.5

So, the correct option is d.