See in the image i got a 1(min term) at the bottom right corner which I can't assign it to any groups . What should i do ? Should i leave this 1 as it is and do other simplification or i should count it as single group ?
You create groups with the size of 2^N elements, this includes the size 1
.(1=2^0). So you create indeed a single group with only that single element at AB'CD'
.