In the first pattern, difference in the consecutive elements kept decreasing by 1
12-8 = 4
8-5 = 3
5-3 = 2
So, last number = 3-1 = 2
In the second pattern, one letter is skipped everytime. So, g comes after e.
In the third pattern, three letters are skipped everytime. So, o comes after k.
In the fourth pattern, every number is multiplied by 3 to get the successive number. So, missing number = 3/3 = 1