If ' x ' stands for ' + ', ' < ' for ' - ', ' + ', for ' ÷ ', ' > ' for ' x ', ' - ' for ' = ', ' ÷ ' for ' > ' and ' = ' for ' < '. then satae which of the following is true .

Try all option one by one;
From option (d),
6 * 4 * 12 * 12
Change the sign, as per the question,
6 x 4 - 12 = 12
Apply the BODMAS rule
After Multiplication
24 - 12 = 12
After Substraction
?     &nbsp12 = 12

Try all option one by one;
From option ( b )
49 - 7 + 3 ÷ 5 x 8 = 24
Change the sign, as per the question,
49 ÷ 7 x 3 - 5 + 8 = 24
Apply the BODMAS rule
B - Brackets first
O - Orders (i.e. Powers and Square Roots, etc.)
DM - Division and Multiplication (left-to-right)
AS - Addition and Subtraction (left-to-right)
Now Applying the BODMAS rule one by one.
49 ÷ 7 x 3 - 5 + 8 = 24
After Division
7 x 3 - 5 + 8 = 24
After Multiplication
21 - 5 + 8 = 24
After Addition
29 - 5 = 24
After subtraction
24 = 24

16 x 2 ÷ 25 + 7 - 4
After replacing the sign according to the given question
16 ÷ 2 + 25 - 7 x 4
Apply the rule BODMAS
B - Brackets first
O - Orders (i.e. Powers and Square Roots, etc.)
DM - Division and Multiplication (left-to-right)
AS - Addition and Subtraction (left-to-right)
             = 16 ÷ 2 + 25 - 7 x 4
             = 8 + 25 - 28
             = 25 - 20
             = 5

The given letter series in below pattern.
pp q q/qp p p
After completing the pattern, we will get complete letter series.
pp q q /qp p p/ qq q p/qq p q /qq p q

The pattern of given letter series is :-
a d c
Using the same pattern, we will get complete letter series.
a d c / a d c / a dc / a d c / ad c

The sequence is made of repetition of abc in different order, so identify the missing alphabet in abc .
second word is reverse of first word, similar way 4th word is reverse of 3r word.
By option (d),
abc/cba/bca/acb ? bcba

The sequence is made of repetition of two blocks acbd and cadb alternatively.
acbd/cadb/acbd/cadb/acbd ? addddb

The sequence is made of repetition of two blocks cab and bac alternatively.
cab/bac/cab/bac/cab/bac ? acbcb

The word aabcd is formed.
2nd word is made by changing to the 2nd position with next alphabet, similarly
3rd word is made by changing to the 3rd position with next alphabet,
4th word is made by changing to the 4th position with next alphabet.
aabcd/abbcd/abccd/abcdd ? adbbad

The series is formed of two repeated alphabet at start and end but middle alphabet is not repeated. The word is formed with the help of combination of reordering of abc.

aabcc/ccabb/bbcaa ? accba