1.  1, 2, 6, 15, 31, 56, 91
A. 31
B. 91
C. 56
D. 15

Answer: Option B

Explanation:

1, 1 + 12 = 2, 2 + 22 = 6, 6 + 32 = 15, 15 + 42 = 31, 31 + 52 = 56, 56 + 62 = 92

Last number of given series must be 92 not 91.