Remember that
In the arithmetic sequence, the difference between two consecutive terms is called the common difference d.
so
Verify the common difference in each sequence
N 1
a1=-5
a2=-3 1/2=-3.5
a2-a1=-3.5-(-5)=1.5 ------> is not the answer
N 2
a1=2 1/2=2.5
a2=4 1/2=4.5
a2-a1=4,5-2.5=2 ----> is not the answer
N 3
a1=1.5
a2=3
a2-a1=3-1.5=1.5 ----> is not the answer
N 4
a1=-4
a2=-1.5
a2-a1=-1.5-(-4)=2.5 -------> is the answer
therefore
The answer is the option N 4