The given letter series in below pattern.
ab b a
Using the same pattern, we will get complete letter series.

Correct Option: D

The given letter series in below pattern.
ab b a
Using the same pattern, we will get complete letter series.
ab b a/abb a/ a bb a

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)

Correct Option: B

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

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
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)

Correct Option: D

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
⇒      12 = 12

Try All option one by one;
Replace the sign as per question;
After Replacing the Sign Apply the BODMAS Rule.

Correct Option: C

Using the proper symbols in ( c ), we get
5 x 2 ÷ 2 < 10 -4 + 8
After Replacing the Sign Apply the BODMAS Rule.
⇒       5 x 1 < 18 - 4
⇒       5 < 14
which is true .

The sequence is made of repetition of abc in different order, so identify the missing alphabet in abc .

Correct Option: D

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