The common difference of an AP is the difference between any two consecutive terms of the AP.
In the AP 4, -1, -6, -11,...
a1=4 and a2=−1.
But, d=a2−a1=−1−4=−5.
In the AP 5, 4, 3, 2, ...
a1=5 and a2=4.
But, d=a2−a1=4−5 =−1.
In the AP 7, 9, 11, 13, ...
a1=7 and a2=9.
But, d=a2−a1=9−7=2.
In the AP 7, 11, 15, 19, ...
a1=7 and a2=11.
But, d=a2−a1=11−7=4.
In the AP 4, 1, -2, -5, ...
a1=4 and a2=1.
But, d=a2−a1=1−4=−3.
Since −5<−3<−1<2<4, we have the required order.