AZ, GT, MN, __ , YB
In this series letter contain AZ, second letter G. From this we can see that A to G increasing order but Z to T decreasing order. 3^rd letter also maintain same pattern respect to 2^nd letter.
Now, we are considering position of each letter according to the alphabetical order.
A + 6 = G, G +6 = M => M + 6 = S
Z - 6 = T, T - 6 = N => N - 6 = H
So, fourth term will be = SH

J2Z, K4X, 17V, ___, H16R, M22P
Here first letter contain 2 letters and one numeric value.
1^st term of each letter : J K I __ H M
Here j to k increasing order but k to I decreasing order, again h to k also increasing order.
Each step + 1, - 2, + 3, - 4 .....
J + 1 = K, K - 2 = I, I + 3 = L,
L - 4 = H, H + 5 = M,
2^nd term also increases by + 2, + 3, + 4, + 5, order.
2 + 2 = 4, 4 + 3 = 7, 7 + 4 = 11, 11 + 5 = 16,
16 + 6 = 22
3^rd term decreases by 2 fixed order.
Z - 2 = X, X - 2 = V, V - 2 = T
Fourth letter will be L11T.

gfe ____ ig ___ eii___ fei _____gf ____ ii
Above series cannot be solve directly because some alphabet repeated.
So, take each option individually and put it.
Among all 4 given options only option 2 satisfied the series : gfeii/gfeii/....

18514 denotes AHEAD
Means 1 ? A, 8 ? H According to the alphabetical position.
Same as 31385, 3 ? A, , 1 ? C, 3 ? C, 8 ? H, 5 ? E
31385 ? CACHE.

Given sequence is
1, 11, 21, 1211, 111221, ........
Now, analyse the terms -
1^st term = 1
2^nd term - It describes the 1^st term term that is has "one" "one" or 11
3^rd term it describes the 2^nd term that it has "two" "one" or 21
4^th term It describes the 3^rd term that it has "one" "2" and "one" "1" or 1211
5^th term It describes the 4^th term that it has "one" "1" "one" "2" and "two" "1" or 111221
Hence the 6 term would be - "Three" "1", "two" "2" and "one" "1" or 312211

From letters O, I, T, N only one meaningful word 'INTO' can be formed and last letter of this word is O.

From the given word, 'MEDICO' is the only word can be formed.

By using the letters of the given word 'MEASUREMENT' we can form the word MASTER.

By using the letters of given word 'CORRESPONDING'.
'DISCERN' is the only word which can be formed

Clearly, 'IMPASSIVE', cannot be formed by letters of the given word IMPOSSIONABLE due to absence of letter 'V".