The given sequence is based on the following pattern :
52 – 1 = 51
51 – 3 = 48
48 – 5 = 43
43 – 7 = 34 is wrong number . So , 36 is correct number .
........... and so on.

Correct Option: B

The given sequence is based on the following pattern :
52 – 1 = 51
51 – 3 = 48
48 – 5 = 43
43 – 7 = 34 is wrong number . So , 36 is correct number .
36 – 9 = 27
27 – 11 = 16
Hence, 34 is the wrong number.

We can see that All the numbers except 81 are prime numbers.

Correct Option: D

We can see that All the numbers except 81 are prime numbers. So , 81 is required answer .

The given sequence is :
First term = 1³ = 1
Second term = 2³ = 8
Third term = 3³ = 27
Fourth term = 4³ = 84 is wrong term . So , 64 is correct number .
Fifth term = 5³ = 125
........... and so on.

Correct Option: C

The given sequence is :
First term = 1³ = 1
Second term = 2³ = 8
Third term = 3³ = 27
Fourth term = 4³ = 84 is wrong term . So , 64 is correct number .
Fifth term = 5³ = 125
Sixth term = 6³ = 216
Seventh term = 7³ = 343
Clearly, 84 is the wrong number.

The given sequence is based on the following pattern :

Odd position series :-
9 + 3 = 12 , 11 + 3 = 14 , 13 + 3 = ?

Correct Option: B

The given sequence is based on the following pattern :

Odd position series :-
9 + 3 = 12 , 11 + 3 = 14 , 13 + 3 = ?
∴ ? = 16
Even position series :-
12 - 1 = 11 , 14 - 1 = 13 , 16 - 1 = 15
Therefore , the missing term of the sequence is 16 .

The series is based on following pattern :
(1)² + 1 = 2
(2)² + 1 = 5
(5)² + 1 = 26
(26)² + 1 = ?

Correct Option: A

The series is based on following pattern :
(1)² + 1 = 2
(2)² + 1 = 5
(5)² + 1 = 26
(26)² + 1 = ?
∴ ? = 677
Hence , required term in the sequence
= 677