The letters in SIKKIM are moving alternately one step forward and one step backward to get the code.Similary, applying this method in TRAINING we will get UQBHOHOF. Hence, option (D) is the correct answer.

The first letter of MENTION is moving one step backward and the each next two letter are interchanging their position in order to get the code.
M [EN] [TI] [ON]
L [NE] [IT] [NO]
Similary, applying this method to PATTERN, we will get, OTAETNR. Hence, option (C) is the correct answer.

The first letter of FORGE remains same and the second , third, fourth and fifth letters are moving one, two, three and four steps forward respectively to get the code.
F +0 step - F
O +1 step - P
R +2 step - T
G +3 step - J
E +4 step - I
Similary, applying the same method in CULPRIT, we get:
C +0 step - C
U +1 step - V
L +2 step - N
P +3 step - S
R +4 step - V
I +5 step - N
T +6 step - Z
Hence, option (B) is the correct answer.

Each letter of ALTERED is replaced by the letter which occupies the same postion after reverseing the English alphabet, to get the code.
A (1st letter of English alphabet) - Z (First letter of English alphabet in reverse order)
L (12th letter of English alphabet) - O (12th letter of English alphabet in reverse order)
T (20th letter of English alphabet) - G (20th letter of English alphabet in reverse order)
E (5th letter of English alphabet) - V (5th letter of English alphabet in reverse order)
R (18th letter of English alphabet) - I (5th letter of English alphabet in reverse order)
E (5th letter of English alphabet) - V (5th letter of English alphabet in reverse order)
D (4th letter of English alphabet) - W (4th letter of English alphabet in reverse order)
Similary, applying the same method, to RELATED, we will get IVOZGVW. Option (A) is the correct answer.

The letters in COMPUTER are to be written in reverse order and each letter, except the first and the last one, is moving one step forward to get the code.

Each letter of the word is moving three steps forward to get the code.

The letters at odd positions are each moving one step backward, while the letters at even positions are respectively moving six, five, four, three, two, ... steps backward to get the corresponding letters of the code.

The word is divided into groups of three letters each and then the letters in each group are written in a reverse order to get the code.
[CIG][ARE][TTE]-----[GIC][ERA][ETT]
Applying same method to DIRECTION, we get, RIDTCENOI. Hence, option (B) is the correct answer.

First, the first six letters and then the last six letters are written in a reverse order to get the code.
[SUBSTI][TUTION]---------- [ITSBUS][NOITUT]
Similary, [DISTRIBUTION] ----------- [IRTSID][NOITUB]
Hence, option (A) is the correct answer.

The letters of the word are written in a reverse order and then the letters of the second and fourth pairs from the end of the word so formed are reversed in order,to obtain the code.
CONTRIBUTE --------- ETUBIRTNOC (First reversed all letters)--------TN(2nd pair)---------------- UB(4th pair)-------NT(Reversed 2nd pair)----- BU (Reversed 4th pair), we get code, ETBUIRNTOC. Similary, applying same to, POPULARISE, we get,'L' at sixth place from left side. Hence, option (C) is the correct answer.